Function watch 

pub fn watch(
    account: &Account,
    control: &Control,
    every: Duration,
    report: impl FnMut(Result<Report, SyncError>),
)

Syncs an account now, then every every until stopped (see Control::pause: counted on the wall clock; while quiet, only when nudged), each sync reported. After a lasting error (a refused password…) it waits for a nudge instead of ending, then tries again (see fetch::Parked: a refused password, unchanged, not before an hour unless Control::retry).