Add protocol frame codec recovery tests

[thecosmicskye]

Summary

Add deterministic protocol frame codec recovery coverage for malformed frame boundaries, and fix the codec header-size mismatch that prevented existing frame tests from decoding encoded frames.

Fixes #2

Changes

• Align FRAME_HEADER_SIZE with the 20 bytes emitted by FrameEncoder.
• Reject nonzero reserved header bytes instead of silently accepting them.
• Resync the decoder to the next frame magic after malformed header/version/length/reserved input so a later valid frame can still be decoded.
• Add tests for truncated headers, truncated payloads, invalid reserved bytes, oversized payload lengths, checksum mismatch, invalid magic, and recovery to a valid following frame.

Testing

• cargo test --lib
  • PASS: 22 tests passed.
• python3 build.py
  • Generated and committed diagnostic/build-6cf45568.json plus diagnostic/build-6cf45568-part001.logd through part006.logd.
  • Target/backend modules: backend PASS, frontend PASS, market PASS, engine PASS, v2-market-stream PASS, nfc-scanner PASS, openapi-tools PASS.
  • Local prerequisite failures: frailbox failed in existing C code, compliance failed because no Java runtime is installed, and openapi-haskell failed because ghc is unavailable.

Checklist

• Relevant modules affected by these changes build locally
• Tests pass locally
• Diagnostic build log is committed in this PR
• Documentation has been updated, if applicable
• Configuration or schema changes are documented, if applicable
• No generated build artifacts are committed, except the required diagnostic build log
• Changes are scoped to the PR purpose and avoid unrelated cleanup
• Security, privacy, and error-handling implications have been considered

---

• I would like to request that my diagnostic build log is removed before merging

[Peter7896]

Thanks for the PR. This is the closest current candidate for the protocol codec recovery issue.

Before this can be forwarded for upstream bounty review, I need to verify the diagnostic bundle and scope. Please keep the PR focused on issue #2 only, and make sure the diagnostic files are exactly what python3 build.py generated on this branch. If the build script generated split .logd parts, please do not edit them manually; I will check whether the metadata and artifact layout match the upstream validator expectations before forwarding.