Renames signals for consistency

Updates signal names across UI components (checkbox, textbox, and CAN) to use more consistent and descriptive names, improving code readability and maintainability. The 'on_change' and 'on_send' signals are renamed to 'changed' and 'send' respectively.

UI/ui_checkbox.hpp

@@ -19,7 +19,7 @@ class UI_checkbox : public UI_item
     json to_json(size_t id) const override;
 
   signals:
-    void on_change(bool);
+    void changed(bool);
 
   private:
     bool m_checked;