Support Open Ephys fallback binaries

[yoshihito-saito]

Summary

• Extend getWaveformsFromDat MergePoints fallback to read Open Ephys continuous.dat files when merged basename.dat and per-epoch amplifier.dat are missing.
• Infer per-segment file channel counts from MergePoints.timestamps_samples and file size, then drop trailing ADC channels by reading only the first session.extracellular.nChannels channels.
• Apply the same channel-count handling to NeuroScope2 sub-epoch raw-data fallback so Open Ephys acquisition-board files with appended ADC channels display correctly.
• Add a synthetic MATLAB regression fixture/test covering Open Ephys-style nested continuous.dat files with trailing ADC channels.

Validation

• matlab -batch "addpath(genpath(pwd)); results = runtests('tests/test_getWaveformsFromDat_mergepoints.m'); assertSuccess(results);"
• matlab -batch "addpath(genpath(pwd)); issues = checkcode('NeuroScope2.m'); fprintf('checkcode issues: %d\n', numel(issues));" succeeded; it reports 192 existing lint issues in NeuroScope2.m.
• Manual NeuroScope2 check on real Open Ephys data confirmed raw traces display correctly without basename.dat.

Notes

• The PR targets ayalab1/CellExplorer, not the upstream original repository.
• Existing local unstaged changes in calc_CellMetrics/loadSpikes.m and manual_tests/ were intentionally left out of this commit.