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/Bot/Debug/PerfMonitor.cpp

@@ -10,7 +10,7 @@
 PerfMonitorOperation* PerfMonitor::start(PerformanceMetric metric, std::string const name,
                                                        PerformanceStack* stack)
 {
-    if (!sPlayerbotAIConfig->perfMonEnabled)
+    if (!sPlayerbotAIConfig.perfMonEnabled)
         return nullptr;
 
     std::string stackName = name;

src/Bot/Debug/PerfMonitor.h

@@ -11,17 +11,16 @@
 #include <map>
 #include <mutex>
 #include <vector>
-
-#include "Common.h"
+#include <cstdint>
 
 typedef std::vector<std::string> PerformanceStack;
 
 struct PerformanceData
 {
-    uint64 minTime;
-    uint64 maxTime;
-    uint64 totalTime;
-    uint32 count;
+    uint64_t minTime;
+    uint64_t maxTime;
+    uint64_t totalTime;
+    uint32_t count;
     std::mutex lock;
 };
 
@@ -50,21 +49,28 @@ private:
 class PerfMonitor
 {
 public:
-    PerfMonitor(){};
-    virtual ~PerfMonitor(){};
-    static PerfMonitor* instance()
+    static PerfMonitor& instance()
     {
         static PerfMonitor instance;
-        return &instance;
+
+        return instance;
     }
 
-public:
     PerfMonitorOperation* start(PerformanceMetric metric, std::string const name,
                                        PerformanceStack* stack = nullptr);
     void PrintStats(bool perTick = false, bool fullStack = false);
     void Reset();
 
 private:
+    PerfMonitor() = default;
+    virtual ~PerfMonitor() = default;
+
+    PerfMonitor(const PerfMonitor&) = delete;
+    PerfMonitor& operator=(const PerfMonitor&) = delete;
+
+    PerfMonitor(PerfMonitor&&) = delete;
+    PerfMonitor& operator=(PerfMonitor&&) = delete;
+
     std::map<PerformanceMetric, std::map<std::string, PerformanceData*> > data;
     std::mutex lock;
 };