test(kinesis): TEMP diagnose flaky flush

[VarshithaPamisetty]

Temporary: registers a verbose log sink + prints the flush result to capture the per-record PutRecords errorCode behind the intermittent recordsFlushed=0. Do not merge.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 41.25%. Comparing base (d8a895d) to head (e358648).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7297      +/-   ##
==========================================
+ Coverage   40.98%   41.25%   +0.26%     
==========================================
  Files         121      121              
  Lines        8273     8288      +15     
  Branches     3598     3604       +6     
==========================================
+ Hits         3391     3419      +28     
+ Misses       4882     4869      -13     

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