a table group_by was returing Self but should return TableGroupBy (#104)

group_by_returns_TableGroupBy

pyarrow-stubs/__lib_pxi/table.pyi

@@ -545,7 +545,7 @@ class Table(_Tabular[ChunkedArray]):
     def set_column(self, i: int, field_: str | Field, column: Array | list) -> Self: ...
     def rename_columns(self, names: dict[str, str]) -> Self: ...
     def drop(self, columns: str | list[str]) -> Self: ...
-    def group_by(self, keys: str | list[str], use_threads: bool = True) -> Self: ...
+    def group_by(self, keys: str | list[str], use_threads: bool = True) -> TableGroupBy: ...
     def join(
         self,
         right_table: Self,
@@ -603,6 +603,9 @@ class TableGroupBy:
     def aggregate(
         self, aggregations: list[tuple[str, str]] | list[tuple[str, str, FunctionOptions]]
     ) -> Table: ...
+    def _table(self) -> Table: ...
+    @property
+    def _use_threads(self) -> bool: ...
 
 __all__ = [
     "ChunkedArray",