UCX simplify receiving frames in `comm`s (#3651)
UCX simplify receiving frames in `comm`s (#3651)

* Prefix `for`-loop variables with `each_*`

Should make it easier to disambiguate things like `frame` and `frames`
as they are now `each_frame` and `frames`.

* Allocate frames the same way in 0-length case

* Always allocate frames, receive non-trivial ones

* Allocate all frames to fill before receiving

* Filter out non-trivial frames to transmit
blaze/distributed,dask/distributed,dask/distributed,blaze/distributed,dask/distributed,dask/distributed