chore(ci): add ruff and mypy, wire them into CI

Back the shipped py.typed promise with an enforced type check and a linter:

- Add ruff + mypy (+ types-requests) to the dev extras and dev requirements,
  with [tool.ruff]/[tool.mypy] config in pyproject.toml (mypy checks the
  package, not the tests).
- Add a lint job to the Forgejo workflow running ruff check + mypy.
- Fix the issues this surfaced: type FileLock.fd as TextIO | None, add a
  targeted type: ignore for the intentional socket.getaddrinfo monkeypatch,
  and drop an unused import.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_http_ops.py

@@ -15,7 +15,7 @@ from llamacppctl.http_ops import (  # noqa: E402
     check_models,
     wait_until_ready,
 )
-from llamacppctl.schema import PromptConfig, ServerConfig  # noqa: E402
+from llamacppctl.schema import PromptConfig  # noqa: E402
 from tests.test_docker_ops import make_cfg  # noqa: E402