fix: mining nodes no longer report invalid target and now open loot after gather

Two bugs fixed:
1. Retry logic (for Classic) re-sent CMSG_GAMEOBJ_USE at 0.15s while the
   gather cast was in-flight, causing SPELL_FAILED_BAD_TARGETS. Now clears
   pendingGameObjectLootRetries_ as soon as SMSG_SPELL_START shows the player
   started a cast (gather accepted).

2. CMSG_LOOT was sent immediately before the gather cast completed, then
   never sent again — so the loot window never opened. Now tracks the last
   interacted GO and sends CMSG_LOOT in handleSpellGo once the gather spell
   completes, matching how the real client behaves.

include/game/game_handler.hpp

@@ -2778,6 +2778,9 @@ private:
         float timer = 0.0f;
     };
     std::vector<PendingLootOpen> pendingGameObjectLootOpens_;
+    // Tracks the last GO we sent CMSG_GAMEOBJ_USE to; used in handleSpellGo
+    // to send CMSG_LOOT after a gather cast (mining/herbalism) completes.
+    uint64_t lastInteractedGoGuid_ = 0;
     uint64_t pendingLootMoneyGuid_ = 0;
     uint32_t pendingLootMoneyAmount_ = 0;
     float pendingLootMoneyNotifyTimer_ = 0.0f;