Fix RealtimeBox broken API + realtime_box_best_effort.h proper deprecation

[saikishor]

Fixes: #200

@christophfroehlich Thanks for nice summary of the issue.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 73.42%. Comparing base (5db607c) to head (6a0894f).

Files with missing lines	Patch %	Lines
include/realtime_tools/realtime_box.h	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #202      +/-   ##
==========================================
- Coverage   73.47%   73.42%   -0.05%     
==========================================
  Files           7        7              
  Lines         411      414       +3     
  Branches       67       68       +1     
==========================================
+ Hits          302      304       +2     
  Misses         68       68              
- Partials       41       42       +1     

Flag	Coverage Δ
unittests	73.42% <66.66%> (-0.05%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
include/realtime_tools/realtime_box.h	85.24% <66.66%> (-0.97%)	⬇️

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