/// The state of a `LazyComponent`.
///
/// - `Pending` — the factory has not been called yet.
/// - `Loading` — `prefetch()` has been called (or the
/// factory is running synchronously); UI should show a
/// spinner.
/// - `Loaded(T)` — the factory has produced a value;
/// `T::clone()` returns it.
/// - `Failed(String)` — the factory panicked or returned
/// an error message; UI should show an error state.