[ESI] [Cosim] DPI cosim Capnp server polling

[teqdruid]

circt/lib/Dialect/ESI/cosim/cosim_dpi_server/Server.cpp

Line 207 in efd420e

// TODO: Figure out how to do this properly, if possible.

Currently, the capnp DPI server polls for events in order to "listen" for the stop signal. I spent some time trying to get this working properly, but this hack is the best I could do. Ideally, the simulation thread would send a signal to the cosim capnp server through some libkj mechanism. Less ideally but better than what we've got, one would run the libkj event loop with a timeout.

More recently, libkj was documented: https://github.com/capnproto/capnproto/blob/master/kjdoc/tour.md
and a question was asked on how to run the event loop with a timeout: https://groups.google.com/g/capnproto/c/BU8olURJ6fE/m/Do117V12AQAJ?pli=1