Add example of setting Units.resolution in the ecephys tutorial

[h-mayorquin]

Motivation

At the inspector we are working on check_units_resolution_is_set check (NeurodataWithoutBorders/nwbinspector#685), which flags Units tables that contain spike_times but have no resolution set. Users running the inspector on files created by following our tutorials would get this warning with no guidance on how to fix it.

I have added a short section to the ecephys tutorial that sets nwbfile.units.resolution right after the existing add_unit loop, with a brief explanation of what the field means and why it matters. I kept the change minimal to avoid restructuring the existing tutorial flow.

What was the reasoning behind this change? Please explain the changes briefly.

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.
• Have you checked to ensure that there aren't other open Pull Requests for the same change?
• Have you included the relevant issue number using "Fix #XXX" notation where XXX is the issue number? By including "Fix #XXX" you allow GitHub to close issue #XXX when the PR is merged.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.86%. Comparing base (286de2d) to head (de7e3b1).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #2174      +/-   ##
==========================================
- Coverage   95.10%   94.86%   -0.24%     
==========================================
  Files          29       29              
  Lines        2943     2943              
  Branches      443      443              
==========================================
- Hits         2799     2792       -7     
- Misses         86       93       +7     
  Partials       58       58              

Flag	Coverage Δ
integration	72.85% <ø> (ø)
unit	85.08% <ø> (-0.28%)	⬇️

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