AcmeSnapshotsProvider

The provider of the acme-snapshots stores: a third-party backend, written as one outside Wow would write it, on the public store SPI and query facet alone, in a module that opts in to nothing. Found by ServiceLoader.

Its stores hold snapshots only: the log SPI's public closure is checked by the ABI-closure rule, not here, so StoreTck's log specs skip for it by design.