Detect trace conflicts in Kprobe context propagation

[grcevski]

This fix detects conflicts on traces for runtimes that use single threaded queued dispatches, e.g. NodeJS. In these situations there's one worker thread, which uses a queue to pick up work and do all of the communication. Our current kprobes support for matching server -> client spans uses the thread id as an identifier, which ends up being wrong in this scenario.

This fix essentially checks if there's an existing active server span for the same thread it that hasn't finished and if there's one, it marks it as invalid. The client spans pull the server span info, if the span is invalid, they ignore it and generate new trace id. This effectively break the server -> client chain, but at least it doesn't make the last server span a parent of all client spans.

I think we'll be able to full implement support for NodeJS by finding appropriate uprobe we can attach in the node runtime, which will allow us perhaps to find a different identifier for the server span, than the thread id. For now NodeJS will not be able to propagate context.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (1e8f70c) 79.36% compared to head (7b942cd) 45.16%.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #557       +/-   ##
===========================================
- Coverage   79.36%   45.16%   -34.20%     
===========================================
  Files          69       67        -2     
  Lines        5830     5652      -178     
===========================================
- Hits         4627     2553     -2074     
- Misses        982     2950     +1968     
+ Partials      221      149       -72     

Flag	Coverage Δ
integration-test	?
unittests	45.16% <ø> (ø)

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