In debug mode, detect cases of btree comparators that violate transitivity, i.e. comp(A,B) && comp(B,C) -> comp(A,C).

When inserting a new element, we verify that the key is ordered correctly with respect to all the other values on the node, which can be done in constant time.

PiperOrigin-RevId: 523729309
Change-Id: Idb5a5912a9aa5411d086cb9fa76791523046778a