proxy: add log prefix and fix line break
This mimics vkr_log for now.
Now if a render worker crashes at device destruction, the proxy will log like:
proxy: failed to send message: Connection reset by peer
proxy: failed to detach res 200
proxy: failed to send message: Broken pipe
proxy: failed to detach res 201
proxy: failed to send message: Broken pipe
proxy: failed to detach res 204
Edited by Yiwei Zhang