identical request should be able to be refused after grace time elapse

[nineteenthSpring]

I think identical request should be able to be refused after grace time elapse. but I spot that all remain requests have been delegated to clickhouse servers after first request timeout. and no options can be configured. when set grace_time: -1s, the server can't be started. display error: can't load config "/data/service/ck-proxy/config.yml": not a valid duration string: "-1s"

[hagen1778]

Thanks for report! It looks like a bug to me but I can't provide no guarantees when it will be fixed. PR's are welcome. cc @valyala

[gontarzpawel]

Fix for that has been released following the commit #146