fix(python): add backfill/refresh wrappers to namespace classes (#6684)

## Summary

Add Python wrapper methods for `alter_table_backfill_columns` and
`refresh_materialized_view` to both `DirectoryNamespace` and
`RestNamespace` in `python/python/lance/namespace.py`.

PR #6678 added these methods to the Rust PyO3 binding but missed the
Python wrapper layer. Without the wrappers, the `LanceNamespace` ABC's
default `UnsupportedOperationError` is called instead of the Rust
implementation.

## Test plan

- [x] Existing tests pass
- Verified locally that `RestNamespace.__dict__` now contains both
methods

Author: jackye1995

python/python/lance/namespace.py

@@ -20,6 +20,8 @@
     AlterTableAddColumnsResponse,
     AlterTableAlterColumnsRequest,
     AlterTableAlterColumnsResponse,
+    AlterTableBackfillColumnsRequest,
+    AlterTableBackfillColumnsResponse,
     AlterTableDropColumnsRequest,
     AlterTableDropColumnsResponse,
     AlterTransactionRequest,
@@ -77,6 +79,8 @@
     MergeInsertIntoTableRequest,
     MergeInsertIntoTableResponse,
     NamespaceExistsRequest,
+    RefreshMaterializedViewRequest,
+    RefreshMaterializedViewResponse,
     RegisterTableRequest,
     RegisterTableResponse,
     RenameTableRequest,
@@ -788,6 +792,20 @@ def alter_table_drop_columns(
         response_dict = self._inner.alter_table_drop_columns(request.model_dump())
         return AlterTableDropColumnsResponse.from_dict(response_dict)
 
+    def alter_table_backfill_columns(
+        self, request: AlterTableBackfillColumnsRequest
+    ) -> AlterTableBackfillColumnsResponse:
+        """Trigger an async backfill job for a computed column."""
+        response_dict = self._inner.alter_table_backfill_columns(request.model_dump())
+        return AlterTableBackfillColumnsResponse.from_dict(response_dict)
+
+    def refresh_materialized_view(
+        self, request: RefreshMaterializedViewRequest
+    ) -> RefreshMaterializedViewResponse:
+        """Trigger an async materialized view refresh."""
+        response_dict = self._inner.refresh_materialized_view(request.model_dump())
+        return RefreshMaterializedViewResponse.from_dict(response_dict)
+
     # Table tag operations
 
     def list_table_tags(self, request: ListTableTagsRequest) -> ListTableTagsResponse:
@@ -1337,6 +1355,20 @@ def alter_table_drop_columns(
         response_dict = self._inner.alter_table_drop_columns(request.model_dump())
         return AlterTableDropColumnsResponse.from_dict(response_dict)
 
+    def alter_table_backfill_columns(
+        self, request: AlterTableBackfillColumnsRequest
+    ) -> AlterTableBackfillColumnsResponse:
+        """Trigger an async backfill job for a computed column."""
+        response_dict = self._inner.alter_table_backfill_columns(request.model_dump())
+        return AlterTableBackfillColumnsResponse.from_dict(response_dict)
+
+    def refresh_materialized_view(
+        self, request: RefreshMaterializedViewRequest
+    ) -> RefreshMaterializedViewResponse:
+        """Trigger an async materialized view refresh."""
+        response_dict = self._inner.refresh_materialized_view(request.model_dump())
+        return RefreshMaterializedViewResponse.from_dict(response_dict)
+
     # Table tag operations
 
     def list_table_tags(self, request: ListTableTagsRequest) -> ListTableTagsResponse: