network: stateless vote compression

[cce]

Summary

Similar to #4589 this provides single-message vote compression without any shared context between messages. It removes msgpack control characters and field names, reducing the size of votes down to just the values present, plus a 2-byte header. It provides 25% smaller messages on typical votes, compared to 6-7% smaller for zstd, and is >20x faster than zstd's fastest levels.

Test Plan

• Adds options to protocol.RandomizeObject to use for testing encoding/decoding random and 10% empty values (used from vpack_test.go).
• Also uses rapid to generate random votes, wiring them up to regular tests and Go fuzz tests.
• Adds test hook to agreement to check all invocations of makeVote when run during tests
• Adds features to algodump for benchmarking and testing against network data (will submit as separate PR)
• Some testing based on plan from network: proposal payload compression #4589:
  • Unit test checking old + new combinations
  • Manual TwoNodes50Each test with master (m) + feature (f)
  • Manual ThreeNodesEvenDist test with [m]m+f, m+f[f] where [r] is a relay node
  • Manual ThreeNodesEvenDist test with relay running feature and other two nodes on master
  • Perf test

[codecov]

Codecov Report

Attention: Patch coverage is 94.03579% with 30 lines in your changes missing coverage. Please review.

Project coverage is 51.84%. Comparing base (039c933) to head (245cfec).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
protocol/codec_tester.go	26.31%	25 Missing and 3 partials ⚠️
network/vpack/vpack.go	98.83%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6276      +/-   ##
==========================================
+ Coverage   51.65%   51.84%   +0.19%     
==========================================
  Files         649      652       +3     
  Lines       86964    87433     +469     
==========================================
+ Hits        44918    45331     +413     
- Misses      39192    39236      +44     
- Partials     2854     2866      +12     

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[jannotti]

Couple questions so far.