`WorkerGuards` is `!Send`

[Leonid Ryzhyk]

The WorkerGuards struct contains a Box<dyn Any> field, which causes it to be !Send:

timely-dataflow/communication/src/initialize.rs

Line 280 in 06fac10

 _others: Box<dyn Any>, 

This makes it hard to wait for the timely computation to finish from any thread other than the one that created it. I wonder if there is a workaround to this.

Thanks!