DOC: Set __module__ attribute for NA and NaT classes

Fixes Sphinx autodoc showing circular 'alias of' references
for pandas.NA and pandas.NaT by explicitly setting their
__module__ attribute to 'pandas'.

Closes #62185

Author: meet-vasita

pandas/_libs/missing.pyx

@@ -375,9 +375,9 @@ class NAType(C_NAType):
     >>> True | pd.NA
     True
     """
+    __module__ = "pandas"
 
     _instance = None
-    __module__ = "pandas"
 
     def __new__(cls, *args, **kwargs):
         if NAType._instance is None:

pandas/_libs/tslibs/nattype.pyx

@@ -372,6 +372,8 @@ class NaTType(_NaT):
     1         NaT
     """
 
+    __module__ = "pandas"
+
     def __new__(cls):
         cdef _NaT base
 
@@ -1828,11 +1830,7 @@ default 'raise'
     @property
     def tzinfo(self) -> None:
         return None
-    
-    @property
-    def __module__(self) -> str:
-        return "pandas"
-    
+
     def as_unit(self, str unit, bint round_ok=True) -> "NaTType":
         """
         Convert the underlying int64 representation to the given unit.
@@ -1872,7 +1870,6 @@ default 'raise'
 
 
 c_NaT = NaTType()  # C-visible
-c_NaT.__module__ = "pandas"
 NaT = c_NaT        # Python-visible