Speed up Image.point() and Image.point_transform()

[akx]

Refs #9649, #9675, #9736, #9737, #9738, #9739, #9740 (same series, same techniques).

Cf. the aforementioned PRs, this also does a couple other cleanups for performance; on my machine, using ImagingNewDirty gave another +10% on top of the first commit. The last commit would technically allow a compiler to inline the point functions, but given their size, a compiler probably won't.

[codspeed-hq]

Merging this PR will improve performance by 35.95%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 6 improved benchmarks
✅ 325 untouched benchmarks

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	test_point_transform[1024x1024-I]	10.1 ms	5.2 ms	+93.63%
⚡	test_point_transform[1024x1024-F]	7.6 ms	5.2 ms	+46.96%
⚡	test_point_lut[1024x1024-L]	4.9 ms	3.7 ms	+31.84%
⚡	test_point_lut[1024x1024-RGBA]	15.1 ms	12.3 ms	+22.04%
⚡	test_point_lut[1024x1024-RGB]	13.3 ms	11.1 ms	+19.2%
⚡	test_point_lut[1024x1024-LA]	11.4 ms	9.9 ms	+15.67%

Tip

Curious why this is faster? Comment @codspeedbot explain why this is faster on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing akx:faster-point (81444fe) with main (6590b1b)}