chore: Update ._native_series refs

narwhals/_interchange/series.py

@@ -35,6 +35,10 @@ def dtype(self: Self) -> DType:
             self._native_series.dtype, version=self._version
         )
 
+    @property
+    def native(self) -> Any:
+        return self._native_series
+
     def __getattr__(self: Self, attr: str) -> NoReturn:
         msg = (  # pragma: no cover
             f"Attribute {attr} is not supported for metadata-only dataframes.\n\n"

narwhals/_pandas_like/dataframe.py

@@ -424,7 +424,7 @@ def select(self: PandasLikeDataFrame, *exprs: PandasLikeExpr) -> PandasLikeDataF
             )
         new_series = align_series_full_broadcast(*new_series)
         df = horizontal_concat(
-            [s._native_series for s in new_series],
+            [s.native for s in new_series],
             implementation=self._implementation,
             backend_version=self._backend_version,
         )

narwhals/_pandas_like/namespace.py

@@ -290,7 +290,7 @@ def func(df: PandasLikeDataFrame) -> list[PandasLikeSeries]:
                 sep_array = init_value.from_iterable(
                     data=[separator] * len(init_value),
                     name="sep",
-                    index=init_value._native_series.index,
+                    index=init_value.native.index,
                     context=self,
                 )
                 separators = (sep_array.zip_with(~nm, "") for nm in null_mask[:-1])