Function createSessionedStore

Wrap an AdcpStateStore so every operation is isolated to sessionKey.

• ids are prefixed with ${sessionKey}:: before hitting the underlying store.
• writes inject _session_key: sessionKey into the document so list() can filter on it.
• reads/lists strip _session_key before returning documents.
• list filters always AND-in _session_key = sessionKey.

sessionKey and caller ids must match SESSION_KEY_PATTERN — no : characters — so ${sessionKey}::${id} is unambiguous. Payloads may not include the reserved _session_key field.

Use this when every handler's state is scoped to a tenant/brand/session, so you don't have to thread sessionKey through every put/list call.