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/StreamAPI.h

@@ -52,6 +52,9 @@ class StreamAPI : public PhoneAPI
     virtual int32_t runOncePart();
     virtual int32_t runOncePart(char *buf, uint16_t bufLen);
 
+    /// Check the current underlying physical link to see if the client is currently connected
+    virtual bool checkIsConnected() override = 0;
+
   private:
     /**
      * Read any rx chars from the link and call handleToRadio
@@ -73,9 +76,6 @@ class StreamAPI : public PhoneAPI
 
     virtual void onConnectionChanged(bool connected) override;
 
-    /// Check the current underlying physical link to see if the client is currently connected
-    virtual bool checkIsConnected() override = 0;
-
     /**
      * Send the current txBuffer over our stream
      */