Add time duration methods

[h-mayorquin]

Motivation

Previously discussed in slack. One difficulty that users have when building an NWBFile is to understand the overall time organization of the data. There is a push for providing better reporting of this and these methods would be useful in this context.

Checklist

• Did you update CHANGELOG.md with your changes?
• Have you checked our Contributing document?
• Have you ensured the PR clearly describes the problem and the solution?
• Is your contribution compliant with our coding style? This can be checked running ruff check . && codespell from the source directory.
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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.28%. Comparing base (293af8c) to head (d25689e).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #2146      +/-   ##
==========================================
+ Coverage   95.23%   95.28%   +0.04%     
==========================================
  Files          29       29              
  Lines        2876     2905      +29     
  Branches      740      748       +8     
==========================================
+ Hits         2739     2768      +29     
  Misses         83       83              
  Partials       54       54              

Flag	Coverage Δ
integration	73.87% <17.24%> (-0.58%)	⬇️
unit	85.09% <100.00%> (+0.15%)	⬆️

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[bendichter]

This looks great to me, thanks for working on this, @h-mayorquin ! I'd be interested in @oruebel 's thoughts as well

[oruebel]

I'd be interested in @oruebel 's thoughts as well

This is looks overall good to me. I added a few small suggestions, but overall this seems fine to me. I'll let @stephprince do final review and approval.