Clean up and speed up RankFilter

[akx]

Tangentially refs #10041 (but doesn't include that GIL release).

This PR:

• applies the familiar hoist + restrict optimizations to ImagingExpand (which underpins RankFilter), and makes it correct for 16-bpc data
• applies hoist and restrict and other optimizations to RankFilter.c.
  • As a side effect, this cleans up the nearly-single-use IMAGING_PIXEL_<dtype> macros from _imaging.h. They were only used in RankFilter (which no longer does image row pointer acquisition for every pixel) and in 2 places in _imaging.c.
• adds a small special-case loop for Min/Max filters; there was no reason to use the Wirth quickselect to get the minimum or maximum value of a window.
• ports in the special-case 3x3 and 5x5 sort networks from http://ndevilla.free.fr/median/median/src/optmed.c
  • Other kernel sizes and ranks other than median still use the quickselect code.

On my machine, this shows a rather shocking speedup for the common benchmarked cases:

----------------------- benchmark 'filter': 9 tests, 2 sources ----------------------
Name (time in us)                        0001_ad277e2 Min  0002_a84857d Min      ΔMin
-------------------------------------------------------------------------------------
test_rank_filter[1237x811-L-Min3]             26,973.0830          205.1670    -99.2%
test_rank_filter[1237x811-I-Min3]             28,445.0000        1,053.5830    -96.3%
test_rank_filter[1237x811-F-Min3]             30,697.0830        1,074.2090    -96.5%
test_rank_filter[1237x811-L-Median3]          30,811.8340          170.2080    -99.4%
test_rank_filter[1237x811-I-Median3]          33,008.1670          944.3330    -97.1%
test_rank_filter[1237x811-F-Median3]          37,974.1250        1,282.0000    -96.6%
test_rank_filter[1237x811-L-Median5]          99,364.7500          869.5420    -99.1%
test_rank_filter[1237x811-I-Median5]         102,803.1250        4,034.9170    -96.1%
test_rank_filter[1237x811-F-Median5]         123,826.5420        5,647.1250    -95.4%
-------------------------------------------------------------------------------------

Adding support for I;16 images in RankFilter is a small patch on top of it if it's desired, but it felt out of scope for this PR.

[codspeed]

Merging this PR will improve performance by ×4.1

⚠️ 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

⚡ 9 improved benchmarks
✅ 615 untouched benchmarks
⏩ 338 skipped benchmarks¹

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	test_rank_filter[1237x811-L-Min3]	242 ms	10.7 ms	×23
⚡	test_rank_filter[1237x811-F-Min3]	252 ms	29.6 ms	×8.5
⚡	test_rank_filter[1237x811-I-Min3]	264.5 ms	33.4 ms	×7.9
⚡	test_rank_filter[1237x811-F-Median3]	275.9 ms	55 ms	×5
⚡	test_rank_filter[1237x811-L-Median3]	244.4 ms	57.1 ms	×4.3
⚡	test_rank_filter[1237x811-I-Median3]	268.2 ms	69.6 ms	×3.9
⚡	test_rank_filter[1237x811-F-Median5]	566.1 ms	344.8 ms	+64.18%
⚡	test_rank_filter[1237x811-L-Median5]	476.3 ms	366.5 ms	+29.96%
⚡	test_rank_filter[1237x811-I-Median5]	527.3 ms	421 ms	+25.25%

Tip

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

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_{Comparing akx:top-ranking (a84857d) with main (ad277e2)}

Footnotes

1. 338 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. ↩

[akx]

The min/max speedup isn't as drastic on Codspeed - I presume GCC isn't optimizing that well.