refactor: relocate MeshCore tools to examples/meshcore/

MeshCore is a protocol implementation ON TOP of DongLoRa, not part of the
dongle itself. Moving it to examples/ makes the separation clear while
keeping it accessible as a real-world usage example.

.gitignore

@@ -4,4 +4,4 @@
 src/board/mod.rs
 __pycache__/
 .hypothesis/
-corpus/generated/
+examples/meshcore/corpus/generated/