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/StayActions.cpp

@@ -19,7 +19,7 @@ bool StayActionBase::Stay()
     if (bot->GetMotionMaster()->GetCurrentMovementGeneratorType() == FLIGHT_MOTION_TYPE)
         return false;
 
-    uint32 sitDelay = sPlayerbotAIConfig->sitDelay / 1000;
+    uint32 sitDelay = sPlayerbotAIConfig.sitDelay / 1000;
     time_t stayTime = AI_VALUE(time_t, "stay time");
     time_t now = time(nullptr);
     if (!stayTime)
@@ -48,7 +48,7 @@ bool StayAction::isUseful()
     if (stayPosition.isSet())
     {
         const float distance = bot->GetDistance(stayPosition.x, stayPosition.y, stayPosition.z);
-        if (sPlayerbotAIConfig->followDistance)
+        if (sPlayerbotAIConfig.followDistance)
         {
             return false;
         }