test: Add logging in Couchbase3Exerciser to help troubleshoot flaky test runs

[tippmar-nr]

On some runs, it looks like the Couchbase3Exerciser deadlocks or otherwise freezes waiting for an async operation to complete. Logging may help figure out where it's going south.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.18%. Comparing base (e652d61) to head (8f3d16f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3078      +/-   ##
==========================================
- Coverage   82.22%   82.18%   -0.04%     
==========================================
  Files         477      477              
  Lines       30627    30627              
  Branches     3426     3426              
==========================================
- Hits        25182    25171      -11     
- Misses       4644     4656      +12     
+ Partials      801      800       -1     

Flag	Coverage Δ
Agent	83.23% <ø> (-0.04%)	⬇️
Profiler	72.51% <ø> (ø)

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see 4 files with indirect coverage changes

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[chynesNR]

Is the idea to try to repro the failure on this branch, or do you want this in main?

[tippmar-nr]

Is the idea to try to repro the failure on this branch, or do you want this in main?

I'd like to have it in main; the flake only occurs rarely (like in overnight builds...)