rwlock instead of mutex around encoding ids

[danking]

Is this reasonable? I noticed it while staring at Spiral profiles.

[codspeed-hq]

Merging this PR will improve performance by 13.17%

⚡ 2 improved benchmarks
✅ 952 untouched benchmarks
⏩ 1466 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	bitwise_not_vortex_buffer_mut[128]	501.1 ns	442.8 ns	+13.17%
⚡	Simulation	map_each[BufferMut<i32>, 128]	858.1 ns	770.6 ns	+11.36%

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_{Comparing dk/rwlock-session (e5dafff) with develop (e0ce169)}

Footnotes

1. 1466 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. ↩