overload RationalTime.from_seconds with additional rate argument

[apetrynet]

Closes #818

Summarize your change.

Work in progress!!
I'm in over my head here so hacking together an attempt.

Overload RationalTime.from_seconds with an additional "rate" argument to avoid having to rescale value to target rate.

Before PR:

now = datetime.datetime.now()
tod = (now - now.replace(hour=0, minute=0, second=0, microsecond=0)).total_seconds()
rt = otio.opentime.from_seconds(tod).rescaled_to(24)

After PR:

now = datetime.datetime.now()
tod = (now - now.replace(hour=0, minute=0, second=0, microsecond=0)).total_seconds()
rt = otio.opentime.from_seconds(tod, 24)

Reference associated tests.

Tests will be added to the unittests

[codecov-commenter]

Codecov Report

Merging #1118 (81f9a21) into master (0cc00ce) will decrease coverage by 0.01%.
The diff coverage is 87.50%.

@@            Coverage Diff             @@
##           master    #1118      +/-   ##
==========================================
- Coverage   86.20%   86.19%   -0.02%     
==========================================
  Files         191      191              
  Lines       19028    19049      +21     
  Branches     2105     2104       -1     
==========================================
+ Hits        16404    16420      +16     
- Misses       2078     2083       +5     
  Partials      546      546              

Flag	Coverage Δ
unittests	86.19% <87.50%> (-0.02%)	⬇️

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

Impacted Files	Coverage Δ
...lineio/opentime-bindings/opentime_rationalTime.cpp	96.05% <71.42%> (+0.05%)	⬆️
src/opentime/rationalTime.h	90.19% <100.00%> (+0.40%)	⬆️
tests/test_opentime.py	99.72% <100.00%> (+<0.01%)	⬆️
src/opentimelineio/serializableObject.cpp	63.85% <0.00%> (-4.98%)	⬇️
src/opentime/errorStatus.h	100.00% <0.00%> (ø)
src/opentimelineio/typeRegistry.h	100.00% <0.00%> (ø)
src/opentimelineio/stringUtils.cpp	66.66% <0.00%> (ø)
src/opentimelineio/deserialization.cpp	60.33% <0.00%> (ø)
src/opentimelineio/serializableObject.h	89.58% <0.00%> (ø)
... and 4 more

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[apetrynet]

Hi!

All tests seem to pass so I'd like some feedback on this PR. What I'm most concerned about is the pybind11 stuff and if I'm introducing memory leaks etc.
The changes done to the python bindings were done based on tips from this stackoverflow post.

And please let me know if the PR should go back to draft. The review request seemed to remove the draft status.

[ssteinbach]

Looks good, but what do you think about a simpler unit test? Or was there something specific you wanted to achieve with the datetime approach?

[ssteinbach]

LGTM!

Thanks @apetrynet!

-Stephan.