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/Db/PlayerbotDungeonRepository.cpp

@@ -3,9 +3,15 @@
  * and/or modify it under version 3 of the License, or (at your option), any later version.
  */
 
-#include "PlayerbotDungeonRepository.h"
+#include "Log.h"
+#include "Timer.h"
+#include "DatabaseEnv.h"
+#include "Field.h"
+#include "World.h"
+// Required import due to poor implementation by AC
+#include "QueryResult.h"
 
-#include "Playerbots.h"
+#include "PlayerbotDungeonRepository.h"
 
 std::vector<DungeonSuggestion> const PlayerbotDungeonRepository::GetDungeonSuggestions()
 {