Adds serial commands to get stats

- Added formatStatsReply, formatRadioStatsReply, and formatPacketStatsReply methods in MyMesh for both simple_repeater, simple_room_server, and simple_sensor.
- Updated CommonCLI to handle new stats commands.

src/helpers/CommonCLI.h

@@ -66,6 +66,9 @@ public:
   virtual void removeNeighbor(const uint8_t* pubkey, int key_len) {
     // no op by default
   };
+  virtual void formatStatsReply(char *reply) = 0;
+  virtual void formatRadioStatsReply(char *reply) = 0;
+  virtual void formatPacketStatsReply(char *reply) = 0;
   virtual mesh::LocalIdentity& getSelfId() = 0;
   virtual void saveIdentity(const mesh::LocalIdentity& new_id) = 0;
   virtual void clearStats() = 0;