In __verify_page_discard, we verify page consistency between the btree and the page server by checking for mismatches on both sides. This is done by sorting the page ID lists of both the btree and the page server, and then going through both sorted lists to find mismatches.

There is currently an edge case found in WT-15882, where if the page server list has been gone through, and there are still pages to go through in the btree list, we miss out on mismatches on the btree side, and we also include an invalid page as a mismatch on the page server side.

The aim of this ticket is to fix this error so that __verify_page_discard correctly finds all page mismatches.