selectedTime function
Imperative helper: shows a time picker inside a modal sheet and
resolves with the chosen UiTimeValue, or null on cancel.
Requires UiSheetScope.show — kept separate to avoid a circular
import between pickers and surfaces. Callers can wire it up in a
few lines; see the README for the canonical pattern.
Implementation
UiTimeValue selectedTime(DateTime d) =>
UiTimeValue(hour: d.hour, minute: d.minute);