The `CSIVolume` struct has references to allocations that are "denormalized"; we
don't store them on the `CSIVolume` struct but hydrate them on read. Tests
detecting potential state store corruptions found two locations where we're not
copying the volume before denormalizing:
* When garbage collecting CSI volume claims.
* When checking if it's safe to force-deregister the volume.
There are no known user-visible problems associated with these bugs but both
have the potential of mutating volume claims outside of a FSM transaction. This
changeset also cleans up state mutations in some CSI tests so as to avoid having
working tests cover up potential future bugs.
