Add check for units table duration

[bendichter]

Modular PR for #628

[codecov-commenter]

Codecov Report

❌ Patch coverage is 95.65217% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 76.89%. Comparing base (d8382c9) to head (28d0303).

Files with missing lines	Patch %	Lines
src/nwbinspector/checks/_ecephys.py	95.65%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #636      +/-   ##
==========================================
+ Coverage   73.03%   76.89%   +3.86%     
==========================================
  Files          47       47              
  Lines        1587     1610      +23     
==========================================
+ Hits         1159     1238      +79     
+ Misses        428      372      -56     

Files with missing lines	Coverage Δ
src/nwbinspector/checks/__init__.py	100.00% <ø> (ø)
src/nwbinspector/checks/_ecephys.py	97.43% <95.65%> (-0.75%)	⬇️

... and 4 files with indirect coverage changes

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