Fix threadmark read tracking was not pruned when a threadmark or thread was deleted
Fix CLI command xf-rebuild:threadmarks-read-tracking being largely non-functional and performing very poorly
Improve threadmark read tracking to more aggressively prune threadmark read into a single last read value to better control bloat of the xf_sv_threadmark_read table
Support using MultiPrefix when rendering thread titles in threadmark overview for a thread, this also avoids triggering a minor php 8 compatibility issue in XenForo code