Speed up rectangle, polygon and line drawing

[akx]

Since hline is the primitive used for scanline-filling polygons, this will speed that up too (especially in the translucent cases), there's just no benchmark for it (yet? I can add one).

In the RGB(A) hline case, the speedup is unswitch (two unswitches actually) and autovectorization.

And the -97.3% reduction below is just... not painting when the ink is entirely translucent. 😄

Note

Stacked on #9982 now because they touch the same things, but that one's primarily a correctness fix. It's probably easier to review that first, then I can rebase this.

[codspeed]

Merging this PR will improve performance by ×3

⚠️ 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

⚡ 4 improved benchmarks
✅ 620 untouched benchmarks
⏩ 338 skipped benchmarks¹

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	test_draw_lines_blend[1237x811-0]	1,028 µs	85.4 µs	×12
⚡	test_draw_lines[1237x811-L]	912.5 µs	380.2 µs	×2.4
⚡	test_draw_lines_blend[1237x811-255]	1,025.2 µs	460.9 µs	×2.2
⚡	test_draw_lines_blend[1237x811-127]	1,025.7 µs	768.3 µs	+33.51%

Tip

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

---

_{Comparing akx:faster-rect-and-line (d06bef6) with main (4b03987)}

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. ↩