MAINT: Use mypy recursive type support (#2898)

Recursive types like the following are now supported by mypy:

OutlineType = List[Union[Destination, "OutlineType"]]

However, this recursuve type does not work with the Sphinx documentation generator; update comment to reflect this.

Author: j-t-1

pypdf/types.py

@@ -14,17 +14,18 @@
 from .generic._outline import OutlineItem
 
 BorderArrayType: TypeAlias = List[Union[NameObject, NumberObject, ArrayObject]]
+
 OutlineItemType: TypeAlias = Union[OutlineItem, Destination]
+
 FitType: TypeAlias = Literal[
     "/XYZ", "/Fit", "/FitH", "/FitV", "/FitR", "/FitB", "/FitBH", "/FitBV"
 ]
-# Those go with the FitType: They specify values for the fit
+# These go with the FitType, they specify values for the fit
 ZoomArgType: TypeAlias = Union[NumberObject, NullObject, float]
 ZoomArgsType: TypeAlias = List[ZoomArgType]
 
-# Recursive types like the following are not yet supported by mypy:
+# Recursive types like the following are not yet supported by Sphinx:
 #    OutlineType = List[Union[Destination, "OutlineType"]]
-# See https://github.com/python/mypy/issues/731
 # Hence use this for the moment:
 OutlineType = List[Union[Destination, List[Union[Destination, List[Destination]]]]]
 
@@ -37,6 +38,7 @@
     "/TwoPageLeft",
     "/TwoPageRight",
 ]
+
 PagemodeType: TypeAlias = Literal[
     "/UseNone",
     "/UseOutlines",
@@ -45,6 +47,7 @@
     "/UseOC",
     "/UseAttachments",
 ]
+
 AnnotationSubtype: TypeAlias = Literal[
     "/Text",
     "/Link",