ddc-core-flow: change initial element of fold to (ExpF, Maybe scalar reference)
ddc-core-flow: start converting clusters program back to ddc
ddc-core-flow: Ext binds now only have one result.

in the paper, external binds could have many outputs. this makes sense,
but adds some accidental complexity.
when converting ddc bindings, there's only ever one binding, so we can
kill this and remove a lot of cruft.
ddc-core-flow: minor cleanup of exp reconstruction
ddc-core-flow: fix types and output of kloks
update tests
ddc-core-flow: lift processes out
ddc-core-flow: oops. fix filters. binder type was wrong for flags
ddc-core: fix type synth bug. consider equivalent types with different names to be subtypes.