refactor: change node count variables from uint8_t to uint16_t (#8478)

This is a non-breaking change that increases the internal representation
of node counts from uint8_t (max 255) to uint16_t (max 65535) to support
larger mesh networks, particularly on ESP32-S3 devices with PSRAM.

Changes:
- NodeStatus: numOnline, numTotal, lastNumTotal (uint8_t -> uint16_t)
- ProtobufModule: numOnlineNodes (uint8_t -> uint16_t)
- MapApplet: loop counters changed to size_t for consistency with getNumMeshNodes()
- NodeStatus: Fixed log format to use %u for unsigned integers

Note: Default class methods keep uint32_t for numOnlineNodes parameter
to match the public API and allow flexibility, even though internal node
counts use uint16_t (max 65535 nodes).

This change does NOT affect protobuf definitions, maintaining wire
compatibility with existing clients and devices.

src/mesh/ProtobufModule.h

@@ -13,7 +13,7 @@ template <class T> class ProtobufModule : protected SinglePortModule
     const pb_msgdesc_t *fields;
 
   public:
-    uint8_t numOnlineNodes = 0;
+    uint16_t numOnlineNodes = 0;
     /** Constructor
      * name is for debugging output
      */