Add support for `yearAndMonth` mode

iOS now supports a year/month picker natively.

```swift
if #available(iOS 17.4, *) {
picker.datePickerMode = .yearAndMonth
} else {
picker.datePickerMode = .date
// Technically, iOS did support it, but it had to be set like this.
picker.datePickerMode = .init(rawValue: 4269) ?? .date
}

if #available(iOS 13.4, *) {
picker.preferredDatePickerStyle = .wheels
}
```

Start by locating the plugin's Swift date-picker mode handling and compare it with the issue's iOS availability branches for year/month selection. Verify the supported iOS behavior and confirm that the new yearAndMonth mode works without changing existing date-picker modes.

Written by the indexing model from the issue text.