fix(compare): exclude BAM bin field from core field comparison

[nh13]

Summary

• Exclude the BAM bin field (bytes 10-11) from raw_core_fields_equal so that bin differences between tools no longer cause false core_diff reports
• Add unit tests for core comparison with differing bin values and for the structured comparison with differing bin + tag order

Context

PR #197 replaced RecordBuf-based field-by-field comparison with raw byte comparison. The raw comparison inadvertently included the BAM bin field, which is a BAM-specific index optimization not part of the SAM data model. Different tools (e.g. fgumi vs fgbio) may compute different bin values for the same alignment, causing all records to be flagged as core_diff even when core fields are identical.

Test plan

• New test test_core_equal_different_bin_values — records with identical core fields but different bin values are reported as equal
• New test test_structured_different_bin_different_tag_order — records with different bin and different tag order report core_match=true, tags_match=false, tag_order_match=true
• All existing tests pass (cargo ci-test)
• Formatting and linting pass (cargo ci-fmt && cargo ci-lint)

Fixes #207

[codecov]

Codecov Report

❌ Patch coverage is 96.42857% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 88.06%. Comparing base (91e5af6) to head (6e25f13).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/commands/compare/raw_compare.rs	96.42%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #208      +/-   ##
==========================================
- Coverage   88.06%   88.06%   -0.01%     
==========================================
  Files         113      113              
  Lines       52795    52820      +25     
==========================================
+ Hits        46495    46516      +21     
- Misses       6300     6304       +4     

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[nh13]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: d9aab363-d28b-4d75-ab63-12ad49f10d2e

📥 Commits

Reviewing files that changed from the base of the PR and between 91e5af6 and 6e25f13.

📒 Files selected for processing (1)

• src/commands/compare/raw_compare.rs

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📝 Walkthrough

Walkthrough

The change modifies raw byte comparison logic for BAM core fields by excluding the bin field from equality checks. Two constants define the bin field's offset and length, allowing comparison to concatenate bytes before and after it. The function now validates that aux-data end offsets match before declaring equivalence. Test coverage is expanded to verify records with identical core fields and tag values (but differing bin values or tag ordering) are correctly identified as equivalent.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: excluding the BAM bin field from core field comparison.
Description check	✅ Passed	The description clearly relates to the changeset, explaining the bin field exclusion, test additions, and context from PR #197.
Linked Issues check	✅ Passed	The PR directly addresses issue #207 by excluding the bin field from core comparison, fixing false core_diff reports when only tag order differs.
Out of Scope Changes check	✅ Passed	All changes are scoped to fixing the bin field comparison issue and adding relevant test cases; no unrelated modifications detected.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch nh/fix-compare-bams-tag-order

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