[Feature] fuzzy: per-hash introspection via rspamadm control fuzzyhash

[Feature] fuzzy: per-hash introspection via rspamadm control fuzzyhash

rspamadm control fuzzyhash <128 hex digest> asks all fuzzy workers for
storage-side diagnostics of a specific hash: flag slots and values,
creation time, remaining ttl and, using the persisted shingle set,
slot ownership (owned/foreign/vacant out of total). Ownership directly
answers the key false-positive triage question: can this hash still
produce fuzzy matches, or has its shingle anchor decayed?

Implemented as a new inspect backend API: the redis backend gathers
everything in a single server-side script round trip; sqlite queries
the digests and shingles tables synchronously. The worker control
handler replies asynchronously from the backend callback (the control
pipe is persistent) using the same fd-attachment mechanism as
fuzzy_stat.