Signup abuse detection and blocking 1.15.6

• Improve User Registration log filtering

• Fix error when doing email pattern check on registration

• Fix 'attempt to read property "group_id" on null' error on viewing trophies

• Fix Team Cymru IP to ASN integration failing for ASN's shorter than 4 digits, also a php 8 compatibility fix.

• Fix the "External API query cache time" option was being ignored
• Fix php 8+ compatibility issue with LinkChecker

• Fix MySQL 8+ compatibility when upgrading

• Remove the defunct Apility.Io as an geoip/asn lookup provider.
• Add external API caching support (default cache time is 12 hours, adjustable), with XF cache context support ('spamCheckCache')

• Remove unexpectedly wide locking on user table during multi-account detection

• Fix admincp multi-account list pagination not generating correct links

• Fix SFS and Project HoneyPot lookup being triggered twice
• Fix showing last activity for guests in tickets in moderation queue