Improper singletons migration to clean Meyer's singletons (cherry-pick) (#2082)

# Pull Request

- Applies the clean and corrected singletons, Meyer pattern. (cherry
picked from @SmashingQuasar )

Testing by just playing the game in various ways. Been tested by myself
@Celandriel and @SmashingQuasar
---

## Complexity & Impact

- Does this change add new decision branches?
    - [x] No
    - [ ] Yes (**explain below**)

- Does this change increase per-bot or per-tick processing?
    - [x] No
    - [ ] Yes (**describe and justify impact**)

- Could this logic scale poorly under load?
    - [x] No
    - [ ] Yes (**explain why**)

---

## Defaults & Configuration

- Does this change modify default bot behavior?
    - [x] No
    - [ ] Yes (**explain why**)

---

## AI Assistance

- Was AI assistance (e.g. ChatGPT or similar tools) used while working
on this change?
    - [x] No
    - [ ] Yes (**explain below**)
---

## Final Checklist

- [x] Stability is not compromised
- [x] Performance impact is understood, tested, and acceptable
- [x] Added logic complexity is justified and explained
- [x] Documentation updated if needed

---

## Notes for Reviewers

Anything that significantly improves realism at the cost of stability or
performance should be carefully discussed
before merging.

---------

Co-authored-by: Nicolas Lebacq <nicolas.cordier@outlook.com>
Co-authored-by: Keleborn <22352763+Celandriel@users.noreply.github.com>

src/Ai/Base/Actions/UseItemAction.cpp

@@ -187,7 +187,7 @@ bool UseItemAction::UseItem(Item* item, ObjectGuid goGuid, Item* itemTarget, Uni
     if (bot->isMoving())
     {
         bot->StopMoving();
-        botAI->SetNextCheckDelay(sPlayerbotAIConfig->globalCoolDown);
+        botAI->SetNextCheckDelay(sPlayerbotAIConfig.globalCoolDown);
         return false;
     }
 
@@ -229,7 +229,7 @@ bool UseItemAction::UseItem(Item* item, ObjectGuid goGuid, Item* itemTarget, Uni
                 out << " on " << chat->FormatItem(itemForSpell->GetTemplate());
             }
             uint32 castTime = spellInfo->CalcCastTime();
-            botAI->SetNextCheckDelay(castTime + sPlayerbotAIConfig->reactDelay);
+            botAI->SetNextCheckDelay(castTime + sPlayerbotAIConfig.reactDelay);
         }
 
         break;
@@ -307,7 +307,7 @@ bool UseItemAction::UseItem(Item* item, ObjectGuid goGuid, Item* itemTarget, Uni
     if (!spellId)
         return false;
 
-    // botAI->SetNextCheckDelay(sPlayerbotAIConfig->globalCoolDown);
+    // botAI->SetNextCheckDelay(sPlayerbotAIConfig.globalCoolDown);
     botAI->TellMasterNoFacing(out.str());
     bot->GetSession()->HandleUseItemOpcode(packet);
     return true;
@@ -486,7 +486,7 @@ bool UseRandomQuestItem::Execute(Event event)
 
     bool used = UseItem(item, goTarget, nullptr, unitTarget);
     if (used)
-        botAI->SetNextCheckDelay(sPlayerbotAIConfig->globalCoolDown);
+        botAI->SetNextCheckDelay(sPlayerbotAIConfig.globalCoolDown);
 
     return used;
 }