Reduce code duplication in the email module (#7558)

stdlib/email/mime/application.pyi

@@ -1,11 +1,10 @@
+from collections.abc import Callable
+from email import _ParamsType
 from email.mime.nonmultipart import MIMENonMultipart
 from email.policy import Policy
-from typing import Callable, Union
 
 __all__ = ["MIMEApplication"]
 
-_ParamsType = Union[str, None, tuple[str, str | None, str]]
-
 class MIMEApplication(MIMENonMultipart):
     def __init__(
         self,

stdlib/email/mime/audio.pyi

@@ -1,11 +1,10 @@
+from collections.abc import Callable
+from email import _ParamsType
 from email.mime.nonmultipart import MIMENonMultipart
 from email.policy import Policy
-from typing import Callable, Union
 
 __all__ = ["MIMEAudio"]
 
-_ParamsType = Union[str, None, tuple[str, str | None, str]]
-
 class MIMEAudio(MIMENonMultipart):
     def __init__(
         self,

stdlib/email/mime/base.pyi

@@ -1,10 +1,8 @@
 import email.message
+from email import _ParamsType
 from email.policy import Policy
-from typing import Union
 
 __all__ = ["MIMEBase"]
 
-_ParamsType = Union[str, None, tuple[str, str | None, str]]
-
 class MIMEBase(email.message.Message):
     def __init__(self, _maintype: str, _subtype: str, *, policy: Policy | None = ..., **_params: _ParamsType) -> None: ...

stdlib/email/mime/image.pyi

@@ -1,11 +1,10 @@
+from collections.abc import Callable
+from email import _ParamsType
 from email.mime.nonmultipart import MIMENonMultipart
 from email.policy import Policy
-from typing import Callable, Union
 
 __all__ = ["MIMEImage"]
 
-_ParamsType = Union[str, None, tuple[str, str | None, str]]
-
 class MIMEImage(MIMENonMultipart):
     def __init__(
         self,

stdlib/email/mime/multipart.pyi

@@ -1,12 +1,11 @@
+from collections.abc import Sequence
+from email import _ParamsType
 from email.message import Message
 from email.mime.base import MIMEBase
 from email.policy import Policy
-from typing import Sequence, Union
 
 __all__ = ["MIMEMultipart"]
 
-_ParamsType = Union[str, None, tuple[str, str | None, str]]
-
 class MIMEMultipart(MIMEBase):
     def __init__(
         self,