feat: Implement Immutable durability level

[Veykril]

This durability has slightly special semantics. Values for it are considered unchanging and as such, queries that only rely on inputs of this durability can discard their edges as the query can't possibily be invalidated again.

very WIP, this is just a rebased version of an old branch of mine.

[netlify]

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[codspeed-hq]

CodSpeed Performance Report

Merging #1022 will degrade performances by 6.43%

_{Comparing Veykril:lw-vrslyxmrynxn (f7eb865) with master (c762869)}

Summary

❌ 4 regressions
✅ 9 untouched

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

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
❌	amortized[Input]	2.1 µs	2.3 µs	-6.43%
❌	mutating[10]	13.9 µs	14.7 µs	-5.26%
❌	mutating[20]	14.6 µs	15.3 µs	-4.44%
❌	mutating[30]	14.5 µs	15.3 µs	-5.35%