Review and update Arc placement in Storage

[ikopylov]

Looks like only inner should be wrapped in Arc (https://github.com/qoollo/pearl/blob/master/src/storage/core.rs#L43), because it is actually passed outside. All inner fields like safe, next_blob_id, blobs does not pass outside (from the first glance), so it looks like Arc on them can be safely removed