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/Priest/Action/PriestActions.cpp

@@ -30,11 +30,11 @@ Unit* CastPowerWordShieldOnAlmostFullHealthBelowAction::GetTarget()
         {
             continue;
         }
-        if (player->GetHealthPct() > sPlayerbotAIConfig->almostFullHealth)
+        if (player->GetHealthPct() > sPlayerbotAIConfig.almostFullHealth)
         {
             continue;
         }
-        if (player->GetDistance2d(bot) > sPlayerbotAIConfig->spellDistance)
+        if (player->GetDistance2d(bot) > sPlayerbotAIConfig.spellDistance)
         {
             continue;
         }
@@ -59,11 +59,11 @@ bool CastPowerWordShieldOnAlmostFullHealthBelowAction::isUseful()
         {
             continue;
         }
-        if (player->GetHealthPct() > sPlayerbotAIConfig->almostFullHealth)
+        if (player->GetHealthPct() > sPlayerbotAIConfig.almostFullHealth)
         {
             continue;
         }
-        if (player->GetDistance2d(bot) > sPlayerbotAIConfig->spellDistance)
+        if (player->GetDistance2d(bot) > sPlayerbotAIConfig.spellDistance)
         {
             continue;
         }
@@ -89,7 +89,7 @@ Unit* CastPowerWordShieldOnNotFullAction::GetTarget()
         {
             continue;
         }
-        if (player->GetDistance2d(bot) > sPlayerbotAIConfig->spellDistance)
+        if (player->GetDistance2d(bot) > sPlayerbotAIConfig.spellDistance)
         {
             continue;
         }
@@ -105,4 +105,4 @@ Unit* CastPowerWordShieldOnNotFullAction::GetTarget()
 bool CastPowerWordShieldOnNotFullAction::isUseful()
 {
     return GetTarget();
-}
+}