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/Class/Druid/Action/DruidActions.cpp

@@ -43,8 +43,8 @@ bool CastStarfallAction::isUseful()
     Unit* ccTarget = context->GetValue<Unit*>("current cc target")->Get();
     if (ccTarget && ccTarget->IsAlive())
     {
-        float dist2d = sServerFacade->GetDistance2d(ccTarget, aoePos.GetPositionX(), aoePos.GetPositionY());
-        if (sServerFacade->IsDistanceLessOrEqualThan(dist2d, sPlayerbotAIConfig->aoeRadius))
+        float dist2d = ServerFacade::instance().GetDistance2d(ccTarget, aoePos.GetPositionX(), aoePos.GetPositionY());
+        if (ServerFacade::instance().IsDistanceLessOrEqualThan(dist2d, sPlayerbotAIConfig.aoeRadius))
             return false;
     }
 
@@ -75,7 +75,7 @@ std::vector<NextAction> CastRebirthAction::getPrerequisites()
 bool CastRebirthAction::isUseful()
 {
     return CastSpellAction::isUseful() &&
-           AI_VALUE2(float, "distance", GetTargetName()) <= sPlayerbotAIConfig->spellDistance;
+           AI_VALUE2(float, "distance", GetTargetName()) <= sPlayerbotAIConfig.spellDistance;
 }
 
 Unit* CastRejuvenationOnNotFullAction::GetTarget()
@@ -91,7 +91,7 @@ Unit* CastRejuvenationOnNotFullAction::GetTarget()
         {
             continue;
         }
-        if (player->GetDistance2d(bot) > sPlayerbotAIConfig->spellDistance)
+        if (player->GetDistance2d(bot) > sPlayerbotAIConfig.spellDistance)
         {
             continue;
         }
@@ -107,4 +107,4 @@ Unit* CastRejuvenationOnNotFullAction::GetTarget()
 bool CastRejuvenationOnNotFullAction::isUseful()
 {
     return GetTarget();
-}
+}

src/Ai/Class/Druid/Action/DruidShapeshiftActions.cpp

@@ -36,7 +36,7 @@ bool CastCasterFormAction::isUseful()
 {
     return botAI->HasAnyAuraOf(GetTarget(), "dire bear form", "bear form", "cat form", "travel form", "aquatic form",
                                "flight form", "swift flight form", "moonkin form", nullptr) &&
-           AI_VALUE2(uint8, "mana", "self target") > sPlayerbotAIConfig->mediumHealth;
+           AI_VALUE2(uint8, "mana", "self target") > sPlayerbotAIConfig.mediumHealth;
 }
 
 bool CastCasterFormAction::Execute(Event event)
@@ -59,4 +59,4 @@ bool CastCancelTreeFormAction::Execute(Event event)
 bool CastTreeFormAction::isUseful()
 {
     return GetTarget() && CastSpellAction::isUseful() && !botAI->HasAura(33891, bot);
-}
+}

src/Ai/Class/Druid/Strategy/OffhealDruidCatStrategy.h

@@ -24,4 +24,4 @@
     }
  };
 
- #endif
+ #endif