fix(codegen): split gc_map tests to a sibling file for the 2000-line cap

[proggeramlug]

check_file_size has been red on main since #8948 merged: it takes gc_map.rs to 2047 lines, over the cap.

I prepared this split while reviewing #8948 but pushed it to the wrong remote — #8948 is same-repo (headRepo=PerryTS) and I pushed to a contributor fork the PR does not track, so the unfixed head is what merged. The push succeeded silently, which is why I did not catch it until the next PR's gate run flagged the file.

The fix itself is unchanged: the cfg(test) module moves to gc_map_tests.rs verbatim via the #[path] pattern the tree already uses (1332 + 712 lines).

Validation: codegen 1337/0, cargo fmt clean, scripts/run_lint_gates.sh 57 of 58 including the compile tier — the exception is the pre-existing \${{ }} substitution artifact (#8929).

Summary by CodeRabbit

• Tests
  • Reorganized GC map rewriting tests into a dedicated test module.
  • Preserved coverage for Mach-O, ELF, and COFF formats, address widths, symbol attributes, derived slots, and round-trip validation.
  • No user-facing behavior or production functionality changed.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: b84fe49b-44ca-450e-b949-96faa9ccf4bb

📥 Commits

Reviewing files that changed from the base of the PR and between 23a2113 and 68d4c13.

📒 Files selected for processing (2)

• crates/perry-codegen/src/gc_map.rs
• crates/perry-codegen/src/gc_map_tests.rs

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📝 Walkthrough

Walkthrough

The inline GC map test module moved to gc_map_tests.rs. The extracted tests retain coverage for platform-specific assembly rewriting, stack-map encoding, symbol handling, derived slots, and malformed input validation. Production logic did not change.

Changes

GC map test extraction

Layer / File(s)	Summary
External test module wiring crates/perry-codegen/src/gc_map.rs, crates/perry-codegen/src/gc_map_tests.rs	gc_map.rs loads the test module from the new sibling file. The file defines shared sample assembly fixtures.
Target and assembly rewrite coverage crates/perry-codegen/src/gc_map_tests.rs	Tests cover address widths, target refusal rules, section names, assembler flags, symbol assignments, attributes, and rewritten stack-map output.
Encoding and validation coverage crates/perry-codegen/src/gc_map_tests.rs	Tests cover repeat encoding, foreign registers, derived slots, corrupted streams, missing maps, and truncated headers.

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

✨ 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 fix/gc-map-split

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