docs: simplify rust benchmarks definition

[adriencaccia]

Simplify how rust benchmarks are defined by removing the need to install both criterion and codspeed-criterion-compat, or both bencher and codspeed-bencher-compat.

[codspeed-hq]

CodSpeed Performance Report

Merging #44 will degrade performances by 3.08%

_{Comparing docs/rust-compat (280d7a0) with main (2c67f80)}

Summary

❌ 1 regressions
✅ 53 untouched benchmarks

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

Benchmarks breakdown

	Benchmark	main	docs/rust-compat	Change
❌	fibo_recursive	916.7 ns	945.8 ns	-3.08%

[art049]

As discussed together, we also need to keep the old definition in the docs not to entirely replace the usage.