LMDB key-size audit for a Datalevin store.

A string value longer than `safe-value-length` is stored and pullable but
cannot be bound by value in a `:where` clause, and cannot be looked up as a
`:db.unique/identity`. Datalevin reports no error — the query returns an
empty result, which is indistinguishable from absence.

Contract:
  (audit conn)      => {attr {:max-len n :values n :unique u :over-limit? b}}
  (violations conn) => the sub-map whose :over-limit? is true
  (value-safe? s)   => whether one value can be matched by value

Datalevin store-open self-heal. Classify an LMDB open failure and apply a
recovery policy so the store returns to health without operator action.
`heal-and-open!` composes classification + policy + the caller's `open-fn`;
it never opens the db itself, keeping this ns driver-agnostic at compile time.

Datalevin (LMDB) implementation of hive-spi.kg.protocol/IKGStore. Schema,
value-type map, db-path and cache-limit are injected by the host — the store
carries no domain schema or config resolution of its own.