fix: enable and fix full type checking (#509)

* fix: enable and fix fully type checking

* chore: pre-commit autoupdate

* refactor: pull types out to file

cibuildwheel/util.py

@@ -8,14 +8,15 @@ from enum import Enum
 from fnmatch import fnmatch
 from pathlib import Path
 from time import sleep
-from typing import Dict, List, NamedTuple, Optional, Union
+from typing import Dict, List, NamedTuple, Optional
 
 import certifi
 
 from .environment import ParsedEnvironment
+from .typing import PathOrStr
 
 
-def prepare_command(command: str, **kwargs: Union[str, os.PathLike]) -> str:
+def prepare_command(command: str, **kwargs: PathOrStr) -> str:
     '''
     Preprocesses a command by expanding variables like {python}.
 
@@ -119,7 +120,7 @@ class DependencyConstraints:
         else:
             return self.base_file_path
 
-    def __repr__(self):
+    def __repr__(self) -> str:
         return f'{self.__class__.__name__}{self.base_file_path!r})'