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/Raid/Karazhan/Action/RaidKarazhanActions.cpp

@@ -617,7 +617,7 @@ bool NetherspiteBlockRedBeamAction::Execute(Event event)
         if (!wasBlocking)
         {
             std::map<std::string, std::string> placeholders{{"%player", bot->GetName()}};
-            std::string text = sPlayerbotTextMgr->GetBotTextOrDefault(
+            std::string text = PlayerbotTextMgr::instance().GetBotTextOrDefault(
                 "netherspite_beam_blocking_red", "%player is moving to block the red beam!", placeholders);
             bot->Yell(text, LANG_UNIVERSAL);
         }
@@ -700,7 +700,7 @@ bool NetherspiteBlockBlueBeamAction::Execute(Event event)
     if (wasBlocking && !isBlockingNow)
     {
         std::map<std::string, std::string> placeholders{{"%player", bot->GetName()}};
-        std::string text = sPlayerbotTextMgr->GetBotTextOrDefault(
+        std::string text = PlayerbotTextMgr::instance().GetBotTextOrDefault(
             "netherspite_beam_leaving_blue", "%player is leaving the blue beam--next blocker up!", placeholders);
         bot->Yell(text, LANG_UNIVERSAL);
         _wasBlockingBlueBeam[botGuid] = false;
@@ -711,7 +711,7 @@ bool NetherspiteBlockBlueBeamAction::Execute(Event event)
         if (!wasBlocking)
         {
             std::map<std::string, std::string> placeholders{{"%player", bot->GetName()}};
-            std::string text = sPlayerbotTextMgr->GetBotTextOrDefault(
+            std::string text = PlayerbotTextMgr::instance().GetBotTextOrDefault(
                 "netherspite_beam_blocking_blue", "%player is moving to block the blue beam!", placeholders);
             bot->Yell(text, LANG_UNIVERSAL);
         }
@@ -793,7 +793,7 @@ bool NetherspiteBlockGreenBeamAction::Execute(Event event)
     if (wasBlocking && !isBlockingNow)
     {
         std::map<std::string, std::string> placeholders{{"%player", bot->GetName()}};
-        std::string text = sPlayerbotTextMgr->GetBotTextOrDefault(
+        std::string text = PlayerbotTextMgr::instance().GetBotTextOrDefault(
             "netherspite_beam_leaving_green", "%player is leaving the green beam--next blocker up!", placeholders);
         bot->Yell(text, LANG_UNIVERSAL);
         _wasBlockingGreenBeam[botGuid] = false;
@@ -804,7 +804,7 @@ bool NetherspiteBlockGreenBeamAction::Execute(Event event)
         if (!wasBlocking)
         {
             std::map<std::string, std::string> placeholders{{"%player", bot->GetName()}};
-            std::string text = sPlayerbotTextMgr->GetBotTextOrDefault(
+            std::string text = PlayerbotTextMgr::instance().GetBotTextOrDefault(
                 "netherspite_beam_blocking_green", "%player is moving to block the green beam!", placeholders);
             bot->Yell(text, LANG_UNIVERSAL);
         }