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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 52.95%. Comparing base (98a87d4) to head (40664fb).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1871      +/-   ##
==========================================
+ Coverage   52.94%   52.95%   +0.01%     
==========================================
  Files          87       87              
  Lines       12788    12787       -1     
==========================================
+ Hits         6770     6771       +1     
+ Misses       6018     6016       -2     

Flag	Coverage Δ
unittests	52.95% <100.00%> (+0.01%)	⬆️

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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.