Add human-friendly string conversion to the input enum types so they can be serialized to and parsed from text formats like JSON or configuration files. Each type gains a String() method returning the canonical snake_case name (e.g. "key_a", "arrow_down", "shift+ctrl", "middle", "gained") and a pointer-receiver FromString method that mutates the receiver. A top-level NewKeyFromString, NewModsFromString, NewMouseButtonFromString, and NewFocusEventFromString constructor is also provided as a more ergonomic alternative.