Add utility functions for comparison and rounding

[darbyjohnston]

Fixes #1622

This PR adds a few utility functions to RationalTime for comparison and rounding:

• A function that compares whether two RationalTimes have the same value and rate. This is different from the "==" operator which scales the time before comparison (e.g., otime::RationalTime(30.2) == otime::RationalTime(60.4, 2.0)).
• Rounding functions that return the floor(), ceil(), and round() of a RationalTime.

If these seem useful I can also add Python bindings for them.

[codecov-commenter]

Codecov Report

Merging #1623 (0012fe1) into main (45c6cfd) will decrease coverage by 0.08%.
Report is 9 commits behind head on main.
The diff coverage is 84.37%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1623      +/-   ##
==========================================
- Coverage   79.91%   79.84%   -0.08%     
==========================================
  Files         197      197              
  Lines       21731    21792      +61     
  Branches     4339     4358      +19     
==========================================
+ Hits        17367    17399      +32     
- Misses       2213     2232      +19     
- Partials     2151     2161      +10     

Flag	Coverage Δ
py-unittests	79.84% <84.37%> (-0.08%)	⬇️

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Files	Coverage Δ
src/opentime/timeRange.h	98.18% <100.00%> (ø)
tests/test_opentime.py	99.74% <100.00%> (+<0.01%)	⬆️
src/opentime/rationalTime.h	93.61% <87.50%> (-0.71%)	⬇️
...lineio/opentime-bindings/opentime_rationalTime.cpp	58.25% <0.00%> (-2.36%)	⬇️

... and 21 files with indirect coverage changes

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[meshula]

Looking good to me, maybe get a second approval :)

[meshula]

Thanks Darby!