peak - swap axes

[cboulay]

ezmsg-event/src/ezmsg/event/peak.py — Switched from [channel, time] to [time, channel] axis ordering:

• moveaxis(..., ax_idx, -1) → moveaxis(..., ax_idx, 0)
• All shape[-1]/shape[:-1] → shape[0]/shape[1:]
• All cross_idx[-1]/cross_idx[:-1] → cross_idx[0]/cross_idx[1:]
• Slicing data[..., slice] → data[slice] (axis 0)
• Concatenation axis=-1 → axis=0
• Tuple construction reordered to time-first: (time_idx,) + (feat_tuple)
• Pad width reordered: ((0, n_pad),) + ((0, 0),) * ...
• Added sorting step after np.where(b_cross_over): with time-first arrays, np.where returns events sorted by time rather than grouped by feature. A lexsort reorders
  events by feature-first to maintain correctness of the refractory period logic and elapsed tracking.

ezmsg-event/tests/test_peak.py — 3 changes:

• sparse.concatenate(..., axis=1) → axis=0
• feat_inds, samp_inds = nonzero() → samp_inds, feat_inds = nonzero()
• Added lexsort to sort result indices by (feat, samp) for comparison with expected values (which are built channel-by-channel)