Workflow persistence

NPZ / cache persistence for HiFiWorkflow.

_StateIOMixin supplies scan-result NPZ I/O, per-element fit-cache persistence, the ASCII fine-scan table, and scan-state restoration. All NPZ reads are scoped to close their file handles after success or validation failure.

atom_hifi.training.state_io.EL_FIT_CACHE_SCHEMA = 2

el_fit_cache.npz schema version. 1 — pegl excluded noise atoms; a separate forced_idx array carried the

noise-forced structures.

2 — noise reps are deduped and promoted to real groups, so pegl is complete

and forced_idx is gone (issue #63). HDBSCAN schema-1 files cannot be migrated; decaf/kmeans legacy CSR arrays remain readable. Covers without input identity or resolved granularity are recomputed before scan reuse.