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>

Doc/reference/expressions.rst

@@ -1424,6 +1424,8 @@ Note that ``a op1 b op2 c`` doesn't imply any kind of comparison between *a* and
 *c*, so that, e.g., ``x < y > z`` is perfectly legal (though perhaps not
 pretty).
 
+.. _expressions-value-comparisons:
+
 Value comparisons
 -----------------