websockets serve needs to run async to work

[renehorstmann]

Updated the starting of the websockets async server, so that the call to serve is also async. The (newer?) websockets version does not expect a path as argument for the serve function, so that was removed as well.

I also encountered the bug of a not merged pull request (Windows 11 path starting with a '/' like "/C:/Users/...") so I updated this as well.