fix: wire SpellHandler::updateTimers and remove stale cast state members

SpellHandler::updateTimers() was never called after PR #23 extraction,
so cast bar timers, spell cooldowns, and unit cast state timers never
ticked. Also removes duplicate cast/queue/spell members left in
GameHandler that shadowed the SpellHandler versions, and fixes
MovementHandler writing to those stale members on world portal.

Demotes SMSG_SPELL_START/CAST_RESULT debug logs to LOG_DEBUG.

include/game/spell_handler.hpp

@@ -79,6 +79,7 @@ public:
         auto it = unitCastStates_.find(guid);
         return (it != unitCastStates_.end() && it->second.casting) ? &it->second : nullptr;
     }
+    void clearUnitCastStates() { unitCastStates_.clear(); }
 
     // Target cast helpers
     bool isTargetCasting() const;