Add mypy configuration

Check both the package and the tests by default, require type hints on all functions and ignore the missing stubs for paramiko, systemd and dbus.

pyproject.toml

@@ -47,6 +47,16 @@ packages = ["simple_backup"]
 [tool.setuptools.dynamic]
 version = { attr = "simple_backup.__version__" }
 
+[tool.mypy]
+files = ["simple_backup", "tests"]
+disallow_untyped_defs = true
+warn_unused_ignores = true
+
+# No usable stubs (types-paramiko lags behind paramiko 5)
+[[tool.mypy.overrides]]
+module = ["paramiko", "systemd", "dbus"]
+ignore_missing_imports = true
+
 [tool.pytest.ini_options]
 testpaths = ["tests"]
 # Import the repo copy, not an installed one