Own axes retained in processor state; Flatten variable-chunk hash; RangedAggregate coordinate-axis fixes

[cboulay]

Summary

Input axes may be views into an ezmsg transport buffer whose lifetime ends after the current subscriber callback, so any axis object a processor retains across calls must own its memory. This PR audits every _reset_state/template-caching site in the package and fixes the ones that aliased input axes, plus two adjacent bugs found during the audit.

Axes ownership (deep-copy retained axes)

• HybridAxisArrayBuffer: _initialize deep-copies the non-target axes kept in the output template message.
• ConcatProcessor: _build_cached_axes deep-copies cached pass-through axes.
• FilterbankTransformer: template axes were a shallow dict copy that still shared the axis objects; now deep-copied.
• CWTTransformer: template axes now deep-copied.
• RangedAggregateTransformer: ax_vec stored a reference to the input coordinate axis data and read it on later messages (trapezoid x-coordinates, argmin/argmax lookups); now copied.

Audited-clean (no change needed): slicer and affinetransform already copy via np.array(); fir_hilbert copies its delay buffer; window/spectrum/adaptive_lattice_notch cache only scalar-field or freshly-allocated axes; remaining _reset_state implementations cache no message-derived axis objects.

Flatten: variable preserve-axis chunk sizes

_hash_message excluded the preserve-axis length so variable-length time chunks no longer reset state and rebuild the merged output axis; reshape takes the preserve-axis length from each live message.

RangedAggregate: CoordinateAxis band labels were broken

The numeric branch raised NameError (sl_dat unbound) on the first band, and the string branch indexed ax_vec with the band values instead of the matched indices. Labels are now "first - last" of the matched entries.

Tests

• New tests assert outputs reuse one processor-owned axis object rather than aliasing input axes (buffer, concat, filterbank, CWT, ranged-aggregate), including a simulated transport-buffer-reuse case that overwrites the first message's axis memory.
• New coverage for Flatten with varying time-chunk sizes and for RangedAggregate string-label coordinate axes.
• Full unit suite: 3617 passed, 5 skipped.