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/WorldBuffAction.cpp

@@ -25,7 +25,7 @@ std::vector<uint32> WorldBuffAction::NeedWorldBuffs(Unit* unit)
 {
     std::vector<uint32> retVec;
 
-    if (sPlayerbotAIConfig->worldBuffs.empty())
+    if (sPlayerbotAIConfig.worldBuffs.empty())
         return retVec;
 
     FactionTemplateEntry const* humanFaction = sFactionTemplateStore.LookupEntry(1);
@@ -70,7 +70,7 @@ std::vector<uint32> WorldBuffAction::NeedWorldBuffs(Unit* unit)
         // If tank, effectiveSpec remains unchanged
     }
 
-    for (auto const& wb : sPlayerbotAIConfig->worldBuffs)
+    for (auto const& wb : sPlayerbotAIConfig.worldBuffs)
     {
         // Faction check
         if (wb.factionId != 0 && wb.factionId != factionId)