Feature Request: Optionally disable immediate evaluation

[wluker]

I've been using PothosUtil --proxy-server along with affinity zones to remotely run flow graphs on an e310. (This is very cool btw.) This works some times but not always and I think it is due to the e310 falling into an inconsistent state with too many semi-concurrent eval calls by the SoapySDR blocks. I think the issue is it takes time to load the fpga bit stream, but eval is called again before it is finished loading. I'm not sure about this, but program lockup on the host as well as remote is common in my experience.

I think it might be useful to be able to turn off the immediate evaluation in PothosFlow. Maybe just a config setting somewhere.