A byte-weighted, sharded, in-memory RangeCacheBackend bounded to a fixed
capacity, built on the standalone foyer-memory crate’s Cache – not the
umbrella foyer crate (which FoyerBackend uses via HybridCache, and
which transitively pulls in a disk-backed storage engine). foyer-memory
is the same in-memory engine HybridCache uses internally for its RAM
tier, so this reuses that eviction implementation without the disk-IO
dependencies, via LfuConfig rather than FoyerBackend’s LruConfig.