TraceId in logs

[approxit]

What I've done:

• Implemented trace_id_var ContextVar as a special variable that can help with tracing logs. Managers background loops have different value, without explicit setup root value is used.
• Added log_level to trace_span to help with log visibility
• Reorganized a little NegotiatingPlugin to have more readable logs

Notable remarks:

• First I've tried using async task name, but it turns out that we have some limited possibilities to rule over their names, as some built-in functions runs new tasks in the background and we can't truly base on them.
• We don't get contents of proposal refusal from providers side. This should be fixed soon

[approxit]

Please run regression tests

Tests are fine as they could be without your rework with child responsibility in managers