refactor: enable more ruff lints and enable ty type checker

[alisterd51]

🧹 Spring cleaning!

Summary of changes:

• Added several new Ruff lints
• Migrated type checker from mypy to ty
• Removed obsolete type annotations
• Updated dev tooling & dependencies
• Updated GitHub Actions workflows
• Prepared setup for upcoming Python 3.15 support

Verification:
The code has been validated with:

ruff check
ruff check --preview
ruff format
ty check
pytest --benchmark-skip

# Only for the commit prior to the ty migration:
mypy --show-traceback

All changes are trivial and were performed either manually or via Ruff/ty autofixes.

Note: I was assisted by Gemini 3.6 Flash, conducting several review cycles before opening this PR.

I expect a slight performance boost from these cleanups (even if it's still Python 😉).