ctypes: add __ctype_{be,le}__ class attributes

[jorenham]

These class attributes are used when swapping endianness:

>>> import ctypes as ct
>>> ct.c_double.__ctype_le__ is ct.c_double.__ctype_be__
False

There should be need to distinguish between these little- and big-endian type flavors in typeshed, because as far as I can tell, their interfaces are statically equivalent.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

pwndbg (https://github.com/pwndbg/pwndbg)
+ pwndbg/aglib/heap/structs.py: note: In member "read_field" of class "CStruct2GDB":
+ pwndbg/aglib/heap/structs.py:186: error: Invalid index type "type[_SimpleCData[Any]] | type[_Pointer[Any]] | type[CFuncPtr]" for "dict[type[_SwappableCData], Type]"; expected type "type[_SwappableCData]"  [index]
+ pwndbg/aglib/heap/structs.py: note: In member "fields" of class "CStruct2GDB":
+ pwndbg/aglib/heap/structs.py:217: error: Invalid index type "type[_SimpleCData[Any]] | type[_Pointer[Any]] | type[CFuncPtr]" for "dict[type[_SwappableCData], Type]"; expected type "type[_SwappableCData]"  [index]

pandas (https://github.com/pandas-dev/pandas)
+ pandas/core/computation/ops.py:328: error: Need type annotation for "_binary_ops_dict" (hint: "_binary_ops_dict: dict[<type>, <type>] = ...")  [var-annotated]