Update spike time calculations for scattered non-spiking units

[CodyCBakerPhD]

Update session duration spike-time boundary handling to correctly support multiple non-spiking units scattered throughout a Units table, not just when the first unit is non-spiking.

The implementation now keeps only unit boundaries where cumulative spike count increases, which avoids invalid indexing from repeated boundaries contributed by non-spiking rows while preserving correct min/max spike-time extraction.

Also adds a regression test covering interleaved spiking and non-spiking unit rows to validate the expected session duration behavior.

[codecov]

Codecov Report

❌ Patch coverage is 96.15385% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 76.79%. Comparing base (d114213) to head (1b2db89).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
dandi/pynwb_utils.py	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1871      +/-   ##
==========================================
+ Coverage   76.75%   76.79%   +0.03%     
==========================================
  Files          87       87              
  Lines       12788    12805      +17     
==========================================
+ Hits         9816     9833      +17     
  Misses       2972     2972              

Flag	Coverage Δ
unittests	76.79% <96.15%> (+0.03%)	⬆️

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[CodyCBakerPhD]

@copilot Please add one new test for this case (of having multiple non-spiking units scattered throughout the rows of a untis table)

[Copilot]

@copilot Please add one new test for this case (of having multiple non-spiking units scattered throughout the rows of a untis table)

Added in commit 9acfc582: a new regression test (test_session_duration_with_scattered_non_spiking_units) covering multiple non-spiking units scattered throughout the Units table, plus the corresponding spike-index handling fix in _get_session_duration.

[CodyCBakerPhD]

@yarikoptic I recommend merging #1872 first

[CodyCBakerPhD]

@yarikoptic OK ready - a user needed this to upload some data