fix: Add missing DictionaryArray methods/properties (#226)

## Docs
- https://arrow.apache.org/docs/python/generated/pyarrow.DictionaryArray.html#pyarrow.DictionaryArray.dictionary
- https://arrow.apache.org/docs/python/generated/pyarrow.DictionaryArray.html#pyarrow.DictionaryArray.indices
- https://arrow.apache.org/docs/python/generated/pyarrow.DictionaryArray.html#pyarrow.DictionaryArray.dictionary_decode
- https://arrow.apache.org/docs/python/generated/pyarrow.DictionaryArray.html#pyarrow.DictionaryArray.dictionary_encode

## Fixes
- https://github.com/narwhals-dev/narwhals/blob/c23e56c56630761f0fbc58b575a1c987e57d58d5/narwhals/_arrow/series.py#L787-L798
- https://github.com/narwhals-dev/narwhals/blob/c23e56c56630761f0fbc58b575a1c987e57d58d5/narwhals/_arrow/series_cat.py#L14-L18

Author: dangotbanned

pyarrow-stubs/__lib_pxi/array.pyi

@@ -1581,6 +1581,12 @@ class LargeBinaryArray(Array[scalar.LargeBinaryScalar]):
 class BinaryViewArray(Array[scalar.BinaryViewScalar]): ...
 
 class DictionaryArray(Array[scalar.DictionaryScalar[_IndexT, _BasicValueT]]):
+    def dictionary_encode(self) -> Self: ...  # type: ignore[override]
+    def dictionary_decode(self) -> Array[Scalar[_BasicValueT]]: ...
+    @property
+    def indices(self) -> Array[Scalar[_IndexT]]: ...
+    @property
+    def dictionary(self) -> Array[Scalar[_BasicValueT]]: ...
     @staticmethod
     def from_buffers(  # type: ignore[override]
         type: _BasicValueT,