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/Cmd/PlayerbotCommandServer.cpp

@@ -48,7 +48,7 @@ void session(socket_ptr sock)
         std::string buffer, request;
         while (ReadLine(sock, &buffer, &request))
         {
-            std::string const response = sRandomPlayerbotMgr->HandleRemoteCommand(request) + "\n";
+            std::string const response = sRandomPlayerbotMgr.HandleRemoteCommand(request) + "\n";
             boost::asio::write(*sock, boost::asio::buffer(response.c_str(), response.size()));
             request = "";
         }
@@ -72,19 +72,19 @@ void server(Acore::Asio::IoContext& io_service, short port)
 
 void Run()
 {
-    if (!sPlayerbotAIConfig->commandServerPort)
+    if (!sPlayerbotAIConfig.commandServerPort)
     {
         return;
     }
 
     std::ostringstream s;
-    s << "Starting Playerbots Command Server on port " << sPlayerbotAIConfig->commandServerPort;
+    s << "Starting Playerbots Command Server on port " << sPlayerbotAIConfig.commandServerPort;
     LOG_INFO("playerbots", "{}", s.str().c_str());
 
     try
     {
         Acore::Asio::IoContext io_service;
-        server(io_service, sPlayerbotAIConfig->commandServerPort);
+        server(io_service, sPlayerbotAIConfig.commandServerPort);
     }
 
     catch (std::exception& e)

src/Bot/Cmd/PlayerbotCommandServer.h

@@ -9,17 +9,24 @@
 class PlayerbotCommandServer
 {
 public:
-    PlayerbotCommandServer() {}
-    virtual ~PlayerbotCommandServer() {}
-    static PlayerbotCommandServer* instance()
+    static PlayerbotCommandServer& instance()
     {
         static PlayerbotCommandServer instance;
-        return &instance;
+
+        return instance;
     }
 
     void Start();
+
+private:
+    PlayerbotCommandServer() = default;
+    ~PlayerbotCommandServer() = default;
+
+    PlayerbotCommandServer(const PlayerbotCommandServer&) = delete;
+    PlayerbotCommandServer& operator=(const PlayerbotCommandServer&) = delete;
+
+    PlayerbotCommandServer(PlayerbotCommandServer&&) = delete;
+    PlayerbotCommandServer& operator=(PlayerbotCommandServer&&) = delete;
 };
 
-#define sPlayerbotCommandServer PlayerbotCommandServer::instance()
-
 #endif