use backoff retry for queues

[bill1600]

stop using pthread_cond_timedwait for queues, but just backoff retry instead.
since we've been seeing crashes in pthread_cond_timedwait, test this version.

[codecov]

Codecov Report

Merging #47 into master will increase coverage by 3.52%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #47      +/-   ##
==========================================
+ Coverage   62.44%   65.96%   +3.52%     
==========================================
  Files           3        3              
  Lines         639      620      -19     
  Branches      131      124       -7     
==========================================
+ Hits          399      409      +10     
+ Misses        165      142      -23     
+ Partials       75       69       -6

Impacted Files	Coverage Δ
src/libparodus_queues.c	85.34% <100%> (+19.41%)	⬆️

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 65.96%. Comparing base (fcef57c) to head (ce1b75b).
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #47      +/-   ##
==========================================
+ Coverage   62.44%   65.96%   +3.52%     
==========================================
  Files           3        3              
  Lines         639      620      -19     
  Branches      131      124       -7     
==========================================
+ Hits          399      409      +10     
+ Misses        165      142      -23     
+ Partials       75       69       -6     

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