pub fn new(mut trace: Tr) -> Self {

        let mut logical_compaction = MutableAntichain::new();
        logical_compaction.update_iter(trace.get_logical_compaction().iter().cloned().map(|t| (t,1)));
        let mut physical_compaction = MutableAntichain::new();
        physical_compaction.update_iter(trace.get_physical_compaction().iter().cloned().map(|t| (t,1)));

        TraceBox {
            logical_compaction,
            physical_compaction,
            trace,
        }
    }
Moves an existing trace into a shareable trace wrapper.

The trace may already exist and have non-initial advance and distinguish frontiers. The boxing
process will fish these out and make sure that they are used for the initial read capabilities.
differential-dataflow/src/trace/wrappers/rc.rs