Evaluate CodSpeed for benchmarking in CI

[vytas7]

I talked to @adriencaccia from CodSpeed during EuroPython 2024, and it turns out that they productified the same Gist by @itamarst that #1825 is based upon 😈

CodSpeed is free for open source projects, and it has even by adopted by projects like Ruff.

[itamarst]

I've set up codspeed for Twisted, it's quite nice (and has already caught some regressions, and enabled some optimizations). Recommend lowering the thresholds for what it considers a change, once you have some data.