Add Lock-free Queue

[saikishor]

Fixes #14

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.67%. Comparing base (db891ef) to head (f764bc8).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #253      +/-   ##
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+ Coverage   70.12%   71.67%   +1.55%     
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  Files           8        9       +1     
  Lines         492      519      +27     
  Branches       84       85       +1     
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+ Hits          345      372      +27     
  Misses         92       92              
  Partials       55       55              

Flag	Coverage Δ
unittests	71.67% <100.00%> (+1.55%)	⬆️

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Files with missing lines	Coverage Δ
include/realtime_tools/lock_free_queue.hpp	100.00% <100.00%> (ø)

[christophfroehlich]

TBH, I don't fully understand all the C++ specifics here 😬
But the API seems to be clean from a user perspective, looking at the tests.

• Does this replace the RealtimeBuffer? Or should the RealtimeBuffer be rewritten to use this queue with capacity of 1?
• What is the practical difference between the RealtimeBox and the queue with capacity of 1? Maybe this is clear for some, but I'd need (and appreciate) a user guide when to use what.
• If we deprecate something, we can also add migration notes to this repository and link it on control.ros.org

[christophfroehlich]

I tested that with ros-controls/ros2_controllers#1480, the API works for me!

[saikishor]

I tested that with ros-controls/ros2_controllers#1480, the API works for me!

@christophfroehlich I had to rewrite some parts of tests to reuse rather than copying for every instance. I've add more tests for all constructable types