Fix opcode parsing, interface instanceof, and runtime bugs

[dlunch]

Summary

Fixes 10 bugs found during a codebase-wide analysis, each with a failing test written first (TDD), plus a test-infrastructure fix.

classfile

• invokeinterface/invokedynamic consumed only 2 of 4 operand bytes, misaligning every opcode (and branch target) after them. The existing Interface.class E2E test only passed by accident; the new parser test asserts exact opcode offsets.

jvm / jvm_rust

• instanceof/checkcast always failed against interfaces: interface names were dropped during class loading and is_inherited_from only walked the superclass chain. ClassDefinition now exposes interface_names() and the check covers direct interfaces, loaded superinterfaces, and the superclass chain. Covered by a unit test and a new InterfaceCast E2E class.
• putstatic stored raw stack ints into boolean/byte/char/short fields, panicking on later typed reads from Rust. It now narrows by field descriptor like putfield (shared to_field_type helper).
• JavaLangString::to_rust_string panicked on unpaired surrogates (legal in Java strings); now uses from_utf16_lossy.

java_runtime

• ByteArrayInputStream.mark() stored readlimit instead of the current position, corrupting reset().
• InputStream.skip() always returned n and allocated an n-sized scratch array; now loops with a bounded buffer and returns the actual skipped count.
• Integer.parseInt() panicked on invalid input; now throws NumberFormatException.
• String.substring(begin, end) underflowed on invalid ranges; now throws StringIndexOutOfBoundsException.
• ISO-8859-1 encoding silently truncated chars > 0xFF; now maps them to ? like the JDK.
• Vector.firstElement() returned null on an empty vector; now throws NoSuchElementException.

New runtime classes: NumberFormatException, StringIndexOutOfBoundsException, NoSuchElementException.

test_utils

• DummyFile deep-copied its state on clone, but Runtime::get_file hands out cloned handles — so file position never persisted across reads. It now shares position via Arc<Mutex> like the production File impls, and read honors seek.

Test plan

• Each fix has a test that failed before the fix and passes after.
• cargo test --workspace: all 25 targets pass.
• cargo clippy --workspace --all-targets: no new warnings (one pre-existing approx_constant error at test_string.rs:309 from Implement WIPI String API #155 remains).

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[codecov]

Codecov Report

❌ Patch coverage is 91.37380% with 27 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.53%. Comparing base (f189376) to head (174373e).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...e/src/classes/java/lang/number_format_exception.rs	64.70%	6 Missing ⚠️
.../java/lang/string_index_out_of_bounds_exception.rs	66.66%	6 Missing ⚠️
java_runtime/src/classes/java/lang/string.rs	77.77%	4 Missing ⚠️
...src/classes/java/util/no_such_element_exception.rs	73.33%	4 Missing ⚠️
classfile/tests/test.rs	92.30%	1 Missing ⚠️
java_runtime/src/classes/java/io/input_stream.rs	90.90%	1 Missing ⚠️
...va_runtime/tests/classes/java/lang/test_integer.rs	91.66%	1 Missing ⚠️
...ava_runtime/tests/classes/java/lang/test_string.rs	97.82%	1 Missing ⚠️
...ava_runtime/tests/classes/java/util/test_vector.rs	96.00%	1 Missing ⚠️
jvm_rust/src/class_definition.rs	90.90%	1 Missing ⚠️
... and 1 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #159      +/-   ##
==========================================
+ Coverage   79.46%   80.53%   +1.07%     
==========================================
  Files         178      183       +5     
  Lines        7741     8018     +277     
==========================================
+ Hits         6151     6457     +306     
+ Misses       1590     1561      -29     

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[Copilot]

Pull request overview

This PR fixes multiple JVM/classfile parsing and Java runtime correctness bugs uncovered via codebase-wide analysis, and adds regression tests to prevent reintroductions.

Changes:

• Fix classfile opcode parsing alignment for invokeinterface / invokedynamic and add targeted parser tests.
• Fix JVM runtime type checks for instanceof / checkcast with interfaces and correct putstatic narrowing for small integral field types.
• Fix several java_runtime behavioral bugs (exceptions, substring, charset encoding, skip, mark/reset, Vector.firstElement) and improve test utilities’ file-handle semantics.

Reviewed changes

Copilot reviewed 34 out of 40 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/test_putstatic.rs	Adds regression test ensuring putstatic narrows stack ints to the declared field type.
tests/test_helper/mod.rs	Removes a crate-level dead_code allow in test helper module.
test_utils/src/lib.rs	Fixes DummyFile cloning semantics by sharing position across clones and honoring seek.
test_data/unit/StaticFlag.java	Adds unit-test fixture class for static small-type fields.
test_data/InterfaceCast.txt	Adds expected output for new interface cast E2E test.
test_data/InterfaceCast.java	Adds E2E program covering instanceof/interface cast behavior.
jvm/tests/test_string.rs	Adds regression test for unpaired surrogate handling in string conversion.
jvm/tests/test_is_instance.rs	Adds regression test for is_instance across interface + superclass chains.
jvm/src/runtime/java_lang_string.rs	Makes Java→Rust UTF-16 conversion lossy to avoid panics on invalid UTF-16.
jvm/src/jvm.rs	Extends inheritance checks to include direct interfaces and loaded superinterfaces.
jvm/src/class_definition.rs	Extends ClassDefinition API with interface_names() (default empty).
jvm_rust/src/interpreter.rs	Shares putfield/putstatic narrowing logic via to_field_type helper.
jvm_rust/src/class_definition.rs	Preserves interface names when building class definitions from protos/classfiles.
java_runtime/tests/classes/java/util/test_vector.rs	Adds tests for Vector.firstElement() empty behavior and indexOf(null).
java_runtime/tests/classes/java/lang/test_string.rs	Adjusts floating test constant and adds tests for invalid substring + ISO-8859-1 unmappable chars.
java_runtime/tests/classes/java/lang/test_integer.rs	Adds test asserting parseInt throws NumberFormatException on invalid input.
java_runtime/tests/classes/java/io/test_file_input_stream.rs	Adds tests ensuring sequential reads advance position and skip returns actual skipped count.
java_runtime/tests/classes/java/io/test_data_input_stream.rs	Adds test covering InputStream.skip() behavior via DataInputStream.
java_runtime/tests/classes/java/io/test_byte_array_input_stream.rs	Adds test for ByteArrayInputStream.mark/reset correctness.
java_runtime/tests/classes/java/io/mod.rs	Registers new ByteArrayInputStream test module.
java_runtime/src/loader.rs	Registers newly added runtime exception classes in the runtime loader.
java_runtime/src/classes/java/util/vector.rs	Changes Vector.firstElement() empty behavior to throw NoSuchElementException.
java_runtime/src/classes/java/util/no_such_element_exception.rs	Implements java/util/NoSuchElementException runtime class.
java_runtime/src/classes/java/util.rs	Wires NoSuchElementException into the java.util module exports.
java_runtime/src/classes/java/lang/string.rs	Adds substring range validation + exception, and fixes ISO-8859-1 encoding for >0xFF chars.
java_runtime/src/classes/java/lang/string_index_out_of_bounds_exception.rs	Implements java/lang/StringIndexOutOfBoundsException runtime class.
java_runtime/src/classes/java/lang/number_format_exception.rs	Implements java/lang/NumberFormatException runtime class.
java_runtime/src/classes/java/lang/integer.rs	Makes Integer.parseInt throw NumberFormatException instead of panicking.
java_runtime/src/classes/java/lang.rs	Wires new java.lang exception classes into the module exports.
java_runtime/src/classes/java/io/input_stream.rs	Fixes InputStream.skip() to bound allocations and return actual skipped bytes.
java_runtime/src/classes/java/io/byte_array_input_stream.rs	Fixes ByteArrayInputStream.mark() to store current position (not readlimit).
classfile/tests/test.rs	Adds opcode-offset regression test for invokeinterface parsing alignment.
classfile/src/opcode.rs	Fixes parsing to consume all operand bytes for invokedynamic/invokeinterface; adds unit tests.
Cargo.toml	Adds workspace test_utils as a dev-dependency for integration tests.
Cargo.lock	Updates lockfile for added dev-dependency.

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