apply method
Applies this operation to the current list.
Modifies current in place and returns the effective operation
(e.g. populated with captured state like removed index).
Implementation
@override
MarkerOp apply(List<Marker> list) {
final res = list.removeAtKey(key);
if (!res.removed || res.marker == null) return this;
return copyWith(index: res.index, removed: res.marker);
}