Fix Some Synchronization Issues in Receive Fuzzer

[nibanks]

Description

Updates the receive fuzzer's packet queue to have a lock. Also removes usage of the std::list since it's not really needed.

Also cleaned up some of the code while I was at it.

Testing

Ran locally. CI/CD

Documentation

N/A

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.05%. Comparing base (f5f8534) to head (b310ac0).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4894      +/-   ##
==========================================
- Coverage   87.55%   87.05%   -0.50%     
==========================================
  Files          56       56              
  Lines       17726    17726              
==========================================
- Hits        15520    15432      -88     
- Misses       2206     2294      +88     

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