feat(TestStreamClient): support custom classes for test consumers and producers

[JeroennC]

Useful for more control of testing behavior in our test suite.
Specifically using this to implement a "StoppableTestConsumer" which can be interrupted during the .getone() call from the outside.
This is required to test the graceful shutdown behaviour we've implemented.

Next to that it allows overriding when the queue.task_done() is called, to make TopicManager.join() wait for all events to be fully processed before continuing to stop the stream engine. This prevents us from requiring sleep calls in our tests

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2898233) 96.09% compared to head (0ea7aba) 96.10%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #166   +/-   ##
=======================================
  Coverage   96.09%   96.10%           
=======================================
  Files          23       23           
  Lines         845      847    +2     
=======================================
+ Hits          812      814    +2     
  Misses         33       33           

Flag	Coverage Δ
unittests	96.10% <100.00%> (+<0.01%)	⬆️

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[woile]

Thanks!