BUG: Fix ArrowDtype.itemsize for fixed-width types

Author: meet-vasita

pandas/core/dtypes/dtypes.py

@@ -1642,8 +1642,11 @@ def kind(self) -> str:
     @cache_readonly
     def itemsize(self) -> int:
         """Return the number of bytes in this dtype"""
+        if hasattr(self.pyarrow_dtype, "bit_width"):
+            return self.pyarrow_dtype.bit_width // 8
         return self.numpy_dtype.itemsize
 
+
     def construct_array_type(self) -> type_t[BaseMaskedArray]:
         """
         Return the array type associated with this dtype.
@@ -2307,8 +2310,11 @@ def kind(self) -> str:
     @cache_readonly
     def itemsize(self) -> int:
         """Return the number of bytes in this dtype"""
+        if hasattr(self.pyarrow_dtype, "bit_width"):
+            return self.pyarrow_dtype.bit_width // 8
         return self.numpy_dtype.itemsize
 
+
     def construct_array_type(self) -> type_t[ArrowExtensionArray]:
         """
         Return the array type associated with this dtype.