Continuous integration benchmarking

[wsxrdv]

Use GitHub workflows to check for regressions. For instance https://docs.codspeed.io/ is free for open source projects and supports both Python and Rust.

[wsxrdv]

The benchmarking is there. But there are no thresholds yet. Thus not closing this issue. Documentation for thresholds: https://bencher.dev/docs/explanation/thresholds/