Fix parsing of time_strings lacking leading zeroes

[meshula]

Link the Issue(s) this Pull Request is related to.

#1293

@jchen9 Hi Julian, here's a rework of the existing routine to address the problem you found, and introduce a little more rigor to what is or is not a well-formed time string.

Fixes #1293

Summarize your change.

Describe the reason for the change.

• fixes parsing of time strings without leading zeroes.
• enforces that a negative sign can only appear in the left most position
• implementation does not allocate memory or copy strings
• implementation does not allow exponential notation and other things that std does allow but are inappropriate for time strings
• compatible with strings produced by ffprobe

Reference associated tests.

adds C based tests corresponding to the existing Python based tests.

[codecov-commenter]

Codecov Report

Merging #1297 (219beb0) into main (fb0b86d) will decrease coverage by 0.03%.
The diff coverage is 68.65%.

@@            Coverage Diff             @@
##             main    #1297      +/-   ##
==========================================
- Coverage   86.14%   86.10%   -0.04%     
==========================================
  Files         196      196              
  Lines       19813    19863      +50     
  Branches     2314     2314              
==========================================
+ Hits        17068    17104      +36     
- Misses       2181     2195      +14     
  Partials      564      564              

Flag	Coverage Δ
py-unittests	86.10% <68.65%> (-0.04%)	⬇️

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

Impacted Files	Coverage Δ
src/opentime/rationalTime.h	90.00% <ø> (ø)
src/opentime/rationalTime.cpp	81.71% <68.65%> (-3.89%)	⬇️

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[codecov-commenter]

Codecov Report

Merging #1297 (26ec46a) into main (64b0e31) will decrease coverage by 0.02%.
The diff coverage is 65.55%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1297      +/-   ##
==========================================
- Coverage   86.15%   86.12%   -0.03%     
==========================================
  Files         199      199              
  Lines       20448    20521      +73     
  Branches     2375     2375              
==========================================
+ Hits        17617    17674      +57     
- Misses       2250     2266      +16     
  Partials      581      581              

Flag	Coverage Δ
py-unittests	86.12% <65.55%> (-0.03%)	⬇️

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

Impacted Files	Coverage Δ
src/opentime/rationalTime.h	90.00% <ø> (ø)
src/opentime/rationalTime.cpp	81.91% <61.25%> (-3.69%)	⬇️
tests/test_opentime.py	99.73% <100.00%> (+<0.01%)	⬆️

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[linux-foundation-easycla]

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• ✅ login: meshula / name: Nick Porcino (b19c715, 6640736, 05fdf5f)

Dismissing this review as it was lost when I rebased this change on latest. The review was addressed though :)

[ssteinbach]

Looks good. One little question about naming. Like to see those c++ tests start to fill in!

[ssteinbach]

Lgtm, thanks!