~I will add pre-commit hook later if I find a good one~
Found a nice repo, but it is no longer maintained:
https://github.com/dnephin/pre-commit-golang
So, I implemented the check as a local hook.
There was a data race inside `CoroutineGroup` because internal timer was
used from multiple threads in the methods `asyncWait()` and
`onCoroutineComplete()`. Changing `registerForeign()` to spawn to the
same `yield_context` fixes the problem because now the timer is accessed
only from the same coroutine which has an internal strand.
During debugging I also added websocket support for `request_gun` tool.
