Use Bazel's persistent worker feature for starting/managing the server

[nathaniel-brough]

Firstly, great project. I feel that the user experience here could be improved somewhat by making use of Bazel's persistent worker API.

Using this approach you could start a server/worker automatically in the background and have Bazel manage the client/server communications. This would be an alternative to running the server as a separate Bazel process, beforehand.

As a replacement for the --exec_path flags you are currently using with the server it would be doable to use a Bazel string_flag.

I'm more than happy to contribute with a PR but I could use some guidance if you feel that this would be a useful addition?

[agoessling]

That Bazel feature must be new. It looks like it is a perfect fit for this problem. I definitely think it would be worth a try to see it works well. I feel like the place to start would be to alter VivadoClient (in vivado/tools/vivado_client.py) to directly interact with a ProcessMonitor (in vivado/tools/process_manager.py), bypassing the ProcessServer (e.g. directly calling read and write on ProcessMonitor instead of passing those through a socket). The new entity (VivadoWrapper?) would be responsible for starting and stopping the Vivado process depending on the --persistent_worker flag. Let me know if you have any other questions on where to dig in, and thanks for your interest and suggestion!

[nathaniel-brough]

Sweet I'll open a WIP, pr soon with some updates.