deprecating fnum-based operations in VDH

[keighrim]

fixing #379

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.62%. Comparing base (d918869) to head (968c3dd).
⚠️ Report is 4 commits behind head on develop.

Files with missing lines	Patch %	Lines
mmif/utils/video_document_helper.py	80.00%	23 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## develop #382 +/- ##
===========================================
+ Coverage 73.27% 73.62% +0.34% 
===========================================
Files 27 27 Lines 3121 3204 +83 ===========================================
+ Hits 2287 2359 +72 - Misses 834 845 +11 

Flag	Coverage Δ
unittests	73.62% <80.00%> (+0.34%)	⬆️

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