BUG: is_nan returns True for pd.NA (#31632)

Author: prakhar987

pandas/_libs/missing.pyx

@@ -347,6 +347,7 @@ class NAType(C_NAType):
     """
 
     _instance = None
+    _typ = "<NA>"
 
     def __new__(cls, *args, **kwargs):
         if NAType._instance is None:

pandas/_libs/tslibs/util.pxd

@@ -215,6 +215,8 @@ cdef inline bint is_nan(object val):
     if is_float_object(val):
         fval = val
         return fval != fval
+    if getattr(val, '_typ', None) == "<NA>":  # TODO : Write in seperate function
+        return True
     return is_complex_object(val) and val != val