[core] Migrate to GPIO-based pin numbering

builder/frameworks/arduino.py

@@ -59,7 +59,7 @@ queue.AddLibrary(
     name="board_${VARIANT}",
     base_dir="$VARIANTS_DIR",
     srcs=[
-        "+<${VARIANT}.cpp>",
+        "+<${VARIANT}.c>",
     ],
     # not adding includes since they're added with the base core
 )

builder/utils/ltchiptool.py

@@ -48,6 +48,7 @@ def env_uf2ota(env: Environment, *args, **kwargs):
         f"--lt-version {lt_version}",
         f'--fw "{project_name}:{project_version}"',
         f"--date {int(now.timestamp())}",
+        "--legacy",
         *env["UF2OTA"],
     ]