Fix single-interval ConsolidateIntervals indexing

[ryanharvey1]

A single 1-by-2 interval makes length(intervals) return 2, so ConsolidateIntervals attempts to access done(2) even though there is only one interval. This causes CleanLFP and callers such as auto_theta_cycles to fail when exactly one artefact is detected.

Use size(intervals,1) in both consolidation loops to iterate over interval rows. Add eight regression tests covering single row and column intervals, strict mode, empty input, overlap consolidation and target mapping, touching bounds, and CleanLFP with one amplitude artefact, one derivative artefact, or no artefacts.

Validation: reproduced the original indexing error before the fix; all eight tests pass after the fix in MATLAB R2025a.

results = runtests('test/test_ConsolidateIntervals.m');
assertSuccess(results);