Function to return vtable from an array

[gatesn]

Adds a function to return the vtable from an array.

This is because it better models the future world where Array<V> holds a vtable: V.
After this we need to change the functions on the vtable trait to take &self

[codspeed-hq]

Merging this PR will degrade performance by 12.36%

❌ 2 regressed benchmarks
✅ 1014 untouched benchmarks
⏩ 1522 skipped benchmarks¹

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

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	bench_many_nulls[0.5]	324.3 µs	360.4 µs	-10.02%
❌	Simulation	bench_many_nulls[0.9]	463.1 µs	528.4 µs	-12.36%

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_{Comparing ngates/array-vtable-fn (46c71bb) with develop (8e1fe29)}

Footnotes

1. 1522 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. ↩