feat: support anyio with a Cargo feature

[wyfo]

Asyncio is the standard and de facto main Python async runtime. Among non-standard runtime, only trio seems to have substantial traction, especially thanks to the anyio project. There is indeed a strong trend for anyio (e.g. FastApi), which can justify a dedicated support.

Relates to #1632

Draft based on #3611

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #3612 will not alter performance

_{Comparing wyfo:anyio (3feb111) with main (6c2e6f8)}

Summary

✅ 69 untouched benchmarks