Reduce code duplication in the email module (#7558)

stdlib/email/utils.pyi

@@ -1,7 +1,8 @@
 import datetime
 import sys
+from email import _ParamType
 from email.charset import Charset
-from typing import Union, overload
+from typing import overload
 
 __all__ = [
     "collapse_rfc2231_value",
@@ -21,7 +22,6 @@ __all__ = [
     "unquote",
 ]
 
-_ParamType = Union[str, tuple[str | None, str | None, str]]
 _PDTZ = tuple[int, int, int, int, int, int, int, int, int, int | None]
 
 def quote(str: str) -> str: ...