Better subset representation with BitSet

[yihozhang]

No description provided.

[codspeed-hq]

Merging this PR will degrade performance by 6.7%

❌ 1 regressed benchmark
✅ 43 untouched benchmarks
⏩ 190 skipped benchmarks¹

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	WallTime	tests[taylor51]	4.4 s	4.7 s	-6.7%

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_{Comparing better-subset (1047c16) with reuse-indices (7cb7500)}

Footnotes

1. 190 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. ↩