Remove constraints on Row TypeVar

Remove constraints on Row TypeVar

It's not clear why there is both Tuple[Any, ...] and Any as possible
types for Row and since Any is one possibility it seems that anything is
possible so those constraints appear to be useless.

We can now remove a few '# type: ignore[no-any-return]' in
*Cursor.fetchone(). On the other hand, mypy wants us to declare the type
of 'records' values coming from transformer's load_rows():

    error: Need type annotation for 'records' (hint: "records: List[<type>] = ...")  [var-annotated]