perf(react_compiler): de-monomorphize block rebuilding

[Boshen]

Extract the reactive transform block-rebuilding slow path so it is emitted once instead of once per transform implementation. The in-place fast path remains statically dispatched.

This reduces the arm64 macOS release example's __text by 8,128 bytes and its gzip size by 2,896 bytes.

Checks: cargo test -p oxc_react_compiler; just ready completed lint and check, with one unrelated parallel Oxlint suppression test failing transiently and passing in isolation.

AI assistance was used for implementation and measurement.

[codspeed-hq]

Merging this PR will not alter performance

✅ 10 untouched benchmarks
⏩ 66 skipped benchmarks¹

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_{Comparing agent/react-compiler-transform-size (63db830) with main (4b12840)²}

Footnotes

1. 66 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 main (ec543f2) during the generation of this report, so 4b12840 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩