fix: truncate large frames/messages in test hooks

[mccutchen]

It appears that the test hooks used when running the autobahn test suite can contribute to excessive latency when logging the 8 to 16mb frame and message payloads in some of the extreme test cases. For now, let's truncate payloads over an arbitrary length.

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 3 lines in your changes missing coverage. Please review.

Project coverage is 79.39%. Comparing base (05edf5a) to head (77cbfc6).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
proto.go	66.66%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #16      +/-   ##
==========================================
- Coverage   79.57%   79.39%   -0.19%     
==========================================
  Files           3        3              
  Lines         421      427       +6     
==========================================
+ Hits          335      339       +4     
- Misses         62       64       +2     
  Partials       24       24              

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