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/PhoneAPI.cpp

@@ -122,6 +122,8 @@ void PhoneAPI::close()
         }
         packetForPhone = NULL;
         filesManifest.clear();
+        filesManifest.shrink_to_fit();
+        lastPortNumToRadio.clear();
         fromRadioNum = 0;
         config_nonce = 0;
         config_state = 0;