Improve resource cleanup on connection close (and make server API a unique pointer) (#9799)

* Improve resource cleanup on connection close

* Copilot had some good feedback. Let's just make the api a unique pointer

* Update src/mesh/api/ServerAPI.cpp

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Copilot stupidly suggesting we call protected methods

* Gotta do it in the superclasses as well

* Fix moar

* Refactor MQTT unit test to ensure proper subscription handling and clear side effects

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

src/mesh/http/ContentHandler.h

@@ -27,10 +27,10 @@ class HttpAPI : public PhoneAPI
   public:
     HttpAPI() { api_type = TYPE_HTTP; }
 
+    /// Check the current underlying physical link to see if the client is currently connected
+    virtual bool checkIsConnected() override { return true; } // FIXME, be smarter about this
   private:
     // Nothing here yet
 
   protected:
-    /// Check the current underlying physical link to see if the client is currently connected
-    virtual bool checkIsConnected() override { return true; } // FIXME, be smarter about this
 };