pub fn advance_to(&mut self, time: T) {
        assert!(self.handle.epoch().less_equal(&time));
        assert!(&self.time.less_equal(&time));
        self.time = time;
    }
Advances the logical time for future records.

Importantly, this method does **not** immediately inform timely dataflow of the change. This happens only when
the session is dropped or flushed. It is not correct to use this time as a basis for a computation's `step_while`
method unless the session has just been flushed.
differential-dataflow/src/input.rs