Detect annotation usage in Java classfile analysis (fixes #146)

[jozanek]

Summary

Closes #146.

Extends the Java classfile parser to extract annotation references from all classfile locations, not just RuntimeVisible/InvisibleAnnotations on classes/fields/methods:

Location	JVMS
Parameter annotations	4.7.18
Type annotations (field/return/supertype/…)	4.7.20
Type annotations on locals/casts (nested in Code)	4.7.3
Annotations on record components (nested in Record)	4.7.30
Types referenced by an @interface element default	4.7.22

Details

• Shared core, distinct entry parsers. parseAnnotation/parseElementValue are shared; each attribute shape gets a thin entry parser. Type annotations skip the target_info/type_path prefix before the body.
• Nested recursion. Code and Record attributes are descended into; readNestedAttributes materializes only annotation-bearing sub-attributes and skips the rest in-stream.
• Correct class-literal decoding. class element values (possibly arrays [Lpkg/Foo; or primitives) are decoded via descriptorToTypes instead of string-slicing.
• Robustness. The "warn, don't fail" guard is widened to NonFatal, since nested parsing can surface EOFException on malformed input.

Out of scope: RetentionPolicy.SOURCE annotations are erased by javac and never appear in classfiles — undetectable by design.