refactor(typing): Use Incomplete marker

- `filter` accepts a `list` in some cases
- `group_by` will need `CompliantGroupBy`
  - See also #2184 (comment)

Author: dangotbanned

narwhals/_compliant/dataframe.py

@@ -26,6 +26,7 @@
     import polars as pl
     import pyarrow as pa
     from typing_extensions import Self
+    from typing_extensions import TypeAlias
     from typing_extensions import TypeIs
 
     from narwhals._compliant.expr import EagerExpr
@@ -34,6 +35,8 @@
     from narwhals.typing import _2DArray
     from narwhals.utils import Implementation
 
+    Incomplete: TypeAlias = Any
+
 __all__ = ["CompliantDataFrame", "CompliantLazyFrame", "EagerDataFrame"]
 
 T = TypeVar("T")
@@ -69,10 +72,10 @@ def collect_schema(self) -> Mapping[str, DType]: ...
     def drop(self, columns: Sequence[str], *, strict: bool) -> Self: ...
     def drop_nulls(self, subset: Sequence[str] | None) -> Self: ...
     def estimated_size(self, unit: SizeUnit) -> int | float: ...
-    def filter(self, predicate: CompliantExprT_contra | Any) -> Self: ...
+    def filter(self, predicate: CompliantExprT_contra | Incomplete) -> Self: ...
     def gather_every(self, n: int, offset: int) -> Self: ...
     def get_column(self, name: str) -> CompliantSeriesT: ...
-    def group_by(self, *keys: str, drop_null_keys: bool) -> Any: ...
+    def group_by(self, *keys: str, drop_null_keys: bool) -> Incomplete: ...
     def head(self, n: int) -> Self: ...
     def item(self, row: int | None, column: int | str | None) -> Any: ...
     def iter_columns(self) -> Iterator[CompliantSeriesT]: ...