Add CBOR trace parser helper and smoke test for compression trace error testing (#557)

[Victor-C-Zhang]

Summary:
Add test infrastructure for E2E error propagation testing in compression tracing:

• TraceTestHelpers.hpp: Header-only CBOR trace parser that decodes trace output
  from CCtx::getLatestTrace() into structured C++ types (ParsedTrace,
  ParsedChunk, ParsedCodec, ParsedGraph). Uses the a1cbor decode API with a
  test arena allocator.

• CompressTraceErrorTest.cpp: Smoke test verifying the parse helper works on a
  real successful compression trace.

• COMPRESS_TRACE_ERROR_TEST_PLAN.md: Plan document for implementing error
  propagation tests covering codec failures, graph failures, type conversion
  failures, segmenter failures, and deduplication logic.

Differential Revision: D97033481

Pulled By: Victor-C-Zhang

[meta-codesync]

@Victor-C-Zhang has exported this pull request. If you are a Meta employee, you can view the originating Diff in D97033481.

[meta-codesync]

@Victor-C-Zhang has imported this pull request. If you are a Meta employee, you can view this in D97033481.

[meta-cla]

Hi @Victor-C-Zhang!

Thank you for your pull request.

We require contributors to sign our Contributor License Agreement, and yours needs attention.

You currently have a record in our system, but the CLA is no longer valid, and will need to be resubmitted.

Process

In order for us to review and merge your suggested changes, please sign at https://code.facebook.com/cla. If you are contributing on behalf of someone else (eg your employer), the individual CLA may not be sufficient and your employer may need to sign the corporate CLA.

Once the CLA is signed, our tooling will perform checks and validations. Afterwards, the pull request will be tagged with CLA signed. The tagging process may take up to 1 hour after signing. Please give it that time before contacting us about it.

If you have received this in error or have any questions, please contact us at cla@meta.com. Thanks!