bpo-45530: speed listobject.c's unsafe_tuple_compare() (GH-29076)

Keep track of whether unsafe_tuple_compare() calls are resolved by the very
first tuple elements, and adjust strategy accordingly. This can significantly
cut the number of calls made to the full-blown PyObject_RichCompareBool(),
and especially when duplicates are rare.

Co-authored-by: Łukasz Langa <lukasz@langa.pl>