Add pyrefly as a type checker in pre-commit and dev dependencies

[lolpack]

Summary

• Adds https://github.com/facebook/pyrefly (v0.62.0) as a third type checker alongside pyright and mypy, scoped to test/types/
• Adds pyrefly to the dev dependency group in pyproject.toml
• Adds a pyrefly pre-commit hook in .pre-commit-config.yaml

Motivation

Pyrefly is a new Rust-based Python type checker from Meta. Benchmarking against the existing checkers on test/types/ shows significant speed improvements:

Checker	Avg (5 runs)
mypy (cold)	5.34s
mypy (warm)	0.41s
pyright	0.48s
pyrefly	0.18s

All existing hooks continue to pass. Pyrefly runs cleanly on test/types/ with no configuration needed.

Test plan

• uv run pyrefly check test/types/ - 0 errors
• uv run prek run --all-files - all 11 hooks pass (including new pyrefly hook)
• Benchmarked 5 cold/warm runs per checker to confirm performance numbers

[patrick-kidger]

Sounds good to me! Thanks for the contribution :)