fix(lib): reject blocks with trailing bytes in RLE sections

[hellobertrand]

Ensure strict validation of RLE literal sections by verifying that both the read and write pointers reach their respective expected ends. This prevents potential issues where malformed data containing trailing bytes could be improperly accepted by the decoder.

Includes a new test case to verify that such forged blocks are correctly rejected.

Signed-off-by: Bertrand Lebonnois 5901952+hellobertrand@users.noreply.github.com

Summary by CodeRabbit

• Bug Fixes
  • Improved handling of corrupted compressed data. Blocks with extra or missing RLE literal bytes, including unexpected literal data for an empty output, are now rejected instead of being decoded as valid. This helps prevent malformed data from being silently accepted.

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ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: defaults
• Review profile: CHILL
• Plan: Advanced
• Run ID: 927a678f-0329-4053-84c2-6d246215aedc

📥 Commits

Reviewing files that changed from the base of the PR and between fdad29c and 749ee4d.

📒 Files selected for processing (4)

• src/lib/zxc_decompress.c
• tests/test_common.h
• tests/test_format.c
• tests/test_main.c

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📝 Walkthrough

GLO RLE decoding now rejects literal streams that leave encoded bytes unconsumed, including nonempty streams when no literals are required. A format regression test verifies that a trailing byte causes ZXC_ERROR_CORRUPT_DATA.

Changes: GLO RLE validation

Layer / File(s)	Summary
Decoder validation and regression test src/lib/zxc_decompress.c, tests/test_format.c, tests/test_common.h, tests/test_main.c	The decoder rejects RLE literal streams that do not consume the complete input. The registered regression test adds a trailing byte to a literal section and checks that decoding returns ZXC_ERROR_CORRUPT_DATA.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 749ee

The RLE validation change is mergeable after normal checks.

Pre-merge checks · 5

Passed checks (5 passed)

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main change: rejecting blocks with trailing bytes in RLE sections.
Docstring Coverage		Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 4 files.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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