OAOO __eq__ on DataType

The C++ data_type type implements operator==, so we should use it in
Cython to avoid the definitions ever going out of sync.

python/cudf/cudf/_lib/cpp/types.pxd

@@ -88,8 +88,9 @@ cdef extern from "cudf/types.hpp" namespace "cudf" nogil:
         data_type(const data_type&) except +
         data_type(type_id id) except +
         data_type(type_id id, int32_t scale) except +
-        type_id id() except +
-        int32_t scale() except +
+        type_id id() noexcept
+        int32_t scale() noexcept
+        bool operator==(const data_type&, const data_type&) noexcept
 
     cpdef enum class interpolation(int32_t):
         LINEAR

python/cudf/cudf/_lib/pylibcudf/types.pyx

@@ -47,9 +47,9 @@ cdef class DataType:
         return self.c_obj.scale()
 
     def __eq__(self, other):
-        if not isinstance(other, DataType):
-            return False
-        return self.id() == other.id() and self.scale() == other.scale()
+        return type(self) is type(other) and (
+            self.c_obj == (<DataType>other).c_obj
+        )
 
     @staticmethod
     cdef DataType from_libcudf(data_type dt):