THRIFT-6136: Handle Ruby container size conversion errors

[kpumuk]

Ruby fuzz targets currently suppress integer-conversion errors by matching Ruby exception text. That hides native protocol-decoding problems and is sensitive to message formatting changes between Ruby versions.

This change removes the conversion-error allowlist so the harness ignores only malformed-protocol and truncated-input exceptions. Native and pure Ruby protocol decoding now report Compact Protocol container counts above the signed 32-bit maximum as ProtocolException::SIZE_LIMIT, matching the documented container-size bound.

The native implementation keeps ordinary container-size validation on C fast paths. Focused Binary, accelerated Binary, and Compact container-read benchmarks remained unchanged from master.

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• If a ticket exists: Does your pull request title follow the pattern "THRIFT-NNNN: describe my issue"?
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• Did you do your best to avoid breaking changes? If one was needed, did you label the Jira ticket with "Breaking-Change"?
• If your change does not involve any code, include [skip ci] anywhere in the commit message to free up build resources.

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Pull request overview

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Updates Ruby fuzzing and decoding to stop suppressing integer-conversion errors while correctly validating/handling Compact Protocol container sizes up to the full unsigned 32-bit range, reporting larger sizes as ProtocolException::SIZE_LIMIT.

Changes:

• Remove Ruby fuzz harness allowlist for integer-conversion errors; only ignore protocol/truncation errors.
• Add unsigned-32-bit container size validation in Ruby BaseProtocol#validate_container_size.
• Update native struct decoding (C extension) and Ruby struct decoding to use the shared container-size validation and add specs for the new behavior.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
lib/rb/test/fuzz/fuzz_common.rb	Tightens which exceptions are ignored by fuzzing to avoid hiding decoding bugs.
lib/rb/spec/struct_spec.rb	Adds specs ensuring reads accept >signed-32-bit sizes and reject >u32 sizes.
lib/rb/spec/base_protocol_spec.rb	Adds spec ensuring skip rejects sizes above u32.
lib/rb/lib/thrift/struct_union.rb	Uses protocol-level validate_container_size for map/list/set sizes.
lib/rb/lib/thrift/protocol/base_protocol.rb	Introduces MAX_CONTAINER_SIZE and enforces u32 upper bound.
lib/rb/ext/struct.c	Adds u32-safe container size conversion/validation in native implementation.

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