Enumeration StorageNamespace

Record namespaces used by the core persistence layer (work doc #16).

• identities — learned peer identities (Destination.knownDestinations entries; [time, packet_hash, public_key, app_data, 0], Python-compatible).
• ratchets — per-destination ratchet rings (arrays of X25519 pubs).
• paths — transport path-table entries (next-hop routes).