debugging: async stack traces lack information

If an exception is thrown from an async utility (Channel::receive, timeout, co_spawn) the stack trace will start at the last resume point.
It has no connection to the last co_await point, so there's very little context to debug it.
Debugging to find the crashing code path takes hours even if the crash is reproducible.
If such a stack comes from production and not reproducible it is unlikely to be debugged.

Note: GCD library on macOS with Swift/ObjC supports async stack traces, so we might learn something from it.

See https://github.com/chriskohlhoff/asio/issues/1239