Add FusedType to Shadow.pyi

* `FusedType` for the PEP484's stub file

Cython/Shadow.pyi

@@ -81,3 +81,8 @@ class typedef(CythonType, Generic[_T]):
     def __call__(self, *arg: Any) -> _T: ...
     def __repr__(self) -> str: ...
     __getitem__ = index_type
+
+class _FusedType(CythonType, Genergic[_T]):
+    def __init__(self, Union[py_int, py_long, , py_float, py_complex, Any]) -> None: ...
+
+def fused_type(basetype: _T) -> Type[FusedType[_T]]: ...