perf(allocator): type-erase RawVec::finish_grow inner function

[Boshen]

Remove the type parameter T from the inner grow function since it's
immediately cast to u8 anyway. This reduces monomorphization from 37
copies to 1, saving ~5,500 instructions of code bloat.

Co-Authored-By: Claude Opus 4.5 noreply@anthropic.com

[Boshen]

• perf(allocator): type-erase RawVec::finish_grow inner function #18175 👈 (View in Graphite)
• refactor(allocator): clean up obsolete bumpalo references #18172
• main

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[codspeed-hq]

Merging this PR will not alter performance

✅ 42 untouched benchmarks
⏩ 3 skipped benchmarks¹

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_{Comparing perf/type-erase-raw-vec-grow (ac412b3) with refactor/cleanup-bumpalo-references (8e577de)²}

Footnotes

1. 3 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on refactor/cleanup-bumpalo-references (e041bb8) during the generation of this report, so 702c633 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[Boshen]

Merge activity

• Jan 18, 8:46 AM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Jan 18, 8:46 AM UTC: Boshen added this pull request to the Graphite merge queue.
• Jan 18, 8:53 AM UTC: Merged by the Graphite merge queue.