fix: resolve runtime errors and shadowed variable warnings

- use custom_minimum_size instead of minimum_size on Button (Godot 4.6 API)
- reduce module_resized signal to 3 args to match _save_layout signature
- rename testing_tile refresh param data -> _data (unused)
- rename name -> layout_name in save_layout/switch_layout (shadows Node.name)

plugins/system_monitor/tiles/testing/testing_tile.gd

@@ -17,7 +17,7 @@ func initialize() -> void:
 	_style()
 
 
-func refresh(data: Dictionary) -> void:
+func refresh(_data: Dictionary) -> void:
 	_cycle = (_cycle + 1) % _levels.size()
 	var target: float = _levels[_cycle]