fix: pyarrow clone returned same native object

narwhals/_arrow/dataframe.py

@@ -591,7 +591,14 @@ def collect(
         raise AssertionError(msg)  # pragma: no cover
 
     def clone(self) -> Self:
-        return self._with_native(self.native, validate_column_names=False)
+        native = self.native
+        if self._backend_version < (14, 0, 0):
+            cloned_table = pa.table(
+                {col: native.column(col).combine_chunks() for col in native.column_names}
+            )
+        else:
+            cloned_table = pa.table(native)
+        return self._with_native(cloned_table, validate_column_names=False)
 
     def item(self, row: int | None, column: int | str | None) -> Any:
         from narwhals._arrow.series import maybe_extract_py_scalar

tests/frame/clone_test.py

@@ -11,6 +11,7 @@ def test_clone(constructor_eager: ConstructorEager) -> None:
     df_clone = df.clone()
     assert df is not df_clone
     assert df._compliant_frame is not df_clone._compliant_frame
+    assert df.to_native() is not df_clone.to_native()
     assert_equal_data(df_clone, expected)
     df_clone_mod = df_clone.with_columns((nw.col("a") + nw.col("b")).alias("c"))
     assert_equal_data(df, expected)