Dealing with diamonds old vs new demux

[MingweiSamuel]

Old demux allowed us to combine a bunch of tees/merges into a single operator and eliminate subgraphs. New demux_enum doesn't allow that. Can we make this into an optimization or reason about demux to make this work?

[MingweiSamuel]

• Closures in maps vs closures in demux
• Can we (or why can't we) make something to combine demux/tee and unions to eliminate diamonds?
• How should we think about filters with monotonicity