✨ Add overload for exec method to support text statement

[YuriiMotov]

Currently session.exec(text("")) works, but leads to static type checker error:

error: No overload variant of "exec" of "Session" matches argument type "TextClause"  [call-overload]
note: Possible overload variants:
note:     def [_TSelectParam: Any] exec(self, statement: Select[_TSelectParam], *, params: Union[Mapping[str, Any], Sequence[Mapping[str, Any]], None] = ..., execution_options: Mapping[str, Any] = ..., bind_arguments: Optional[dict[str, Any]] = ..., _parent_execute_state: Optional[Any] = ..., _add_event: Optional[Any] = ...) -> TupleResult[_TSelectParam]
note:     def [_TSelectParam: Any] exec(self, statement: SelectOfScalar[_TSelectParam], *, params: Union[Mapping[str, Any], Sequence[Mapping[str, Any]], None] = ..., execution_options: Mapping[str, Any] = ..., bind_arguments: Optional[dict[str, Any]] = ..., _parent_execute_state: Optional[Any] = ..., _add_event: Optional[Any] = ...) -> ScalarResult[_TSelectParam]
note:     def exec(self, statement: UpdateBase, *, params: Union[Mapping[str, Any], Sequence[Mapping[str, Any]], None] = ..., execution_options: Mapping[str, Any] = ..., bind_arguments: Optional[dict[str, Any]] = ..., _parent_execute_state: Optional[Any] = ..., _add_event: Optional[Any] = ...) -> CursorResult[Any]

This PR adds overload for Session.exec and AsyncSession.exec to fix this.

Addresses #376