* BIG refactor: 'board' and 'radio' objects now defined in 'target.h/.cpp'

* mesh::RTCClock class moved to MeshCore.h

variants/xiao_c3/target.h

@@ -0,0 +1,10 @@
+#pragma once
+
+#include <helpers/XiaoC3Board.h>
+#include <helpers/CustomSX1262Wrapper.h>
+#include <helpers/CustomSX1268Wrapper.h>
+
+extern XiaoC3Board board;
+extern RADIO_CLASS radio;
+
+bool radio_init();