spec: Overview over consensus logic covered with tests

[josef-widder]

• I made a rough overview (rendered) over what consensus we cover now with quint tests.
• Then I added two more tests for cases we didn’t cover before (line 28 and line 42 without locking).
• For the line 28 test, I realised we didn't handle the logic about starting timeoutPrevote properly (in one case). It involved also a fix in the "pending" logic as there is a case where an incoming prevote must trigger execution of line 34 and line 36. So I fixed that in the executor.

Please have a look!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d4090cb) 95.64% compared to head (18ae857) 95.64%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #92   +/-   ##
=======================================
  Coverage   95.64%   95.64%           
=======================================
  Files          31       31           
  Lines        1833     1833           
=======================================
  Hits         1753     1753           
  Misses         80       80           

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