Add documentation for SpikeEventSeries

[stephprince]

Motivation

Fix #1937.

In addition to adding a documentation example for SpikeEventSeries, I updated the "Designating electrophysiology data" section to reflect my understanding of when SpikeEventSeries should be used and the upcoming deprecation to EventWaveform.

I discussed with @oruebel that since there are now optional, predefined columns in the Units table for storing sorted spike waveforms, then I believe SpikeEventSeries should predominantly be used for storing unsorted spiking activity?

How to test the behavior?

cd docs
make clean && make html

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 91.87%. Comparing base (1bdffe8) to head (6930a94).
Report is 1 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #1983   +/-   ##
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  Coverage   91.87%   91.87%           
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  Files          27       27           
  Lines        2697     2697           
  Branches      704      704           
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  Hits         2478     2478           
  Misses        145      145           
  Partials       74       74           

Flag	Coverage Δ
integration	72.71% <ø> (ø)
unit	83.27% <ø> (ø)

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