docs: add pyrefly tabs alongside mypy in type-checking guide

[henryiii]

🤖 AI text below 🤖

Adds Pyrefly as a tabbed alternative to MyPy in the Type checking section of docs/guides/style.md, using the existing mystmd tab-set/tab-item convention with :sync: so the checker choice stays consistent across snippets.

What changed

• Intro prose — notes Pyrefly as a fast Rust-based checker shown alongside MyPy.
• Pre-commit hook — tab-set with the existing MyPy hook and a new Pyrefly tab (facebook/pyrefly-pre-commit, id: pyrefly-check).
• pyproject.toml config — tab-set keeping the full MyPy config (incl. {rr} repo-review codes) and a new Pyrefly tab.

Pyrefly equivalents used

MyPy	Pyrefly
files = "src"	project-includes = ["src"]
python_version	python-version
strict = true	preset = "strict"
[[tool.mypy.overrides]] + ignore_missing_imports	ignore-missing-imports = ["numpy"]
per-code toggles	[tool.pyrefly.errors] table
# type: ignore	# pyrefly: ignore (also honors # type: ignore)

Notes

• docs/guides/mypy.md left untouched — it's a conceptual typing deep-dive (MyPy as the running example), with no tool config that maps to a Pyrefly variant.
• Pyrefly moves fast; the hook is pinned to rev: "1.1.1". Worth confirming the version against repo conventions.
• Verified the page builds cleanly with myst build --html (no warnings).

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📚 Documentation preview 📚: https://scientific-python-cookie--816.org.readthedocs.build/