This is one step closer to sanity in terms of physical files. As per the
comment I have left in place, we really should be checking file sizes or
hashes, but to keep things simple and fast I've opted to just cover the
"missing file" scenario for now.
Ran into this when testing against a foreign `client.realm` by:
- Noticing a beatmap doesn't load
- Deleting said beatmap
- Downloading via beatmap overlay
- Beatmap is restored but still doesn't work
Note that I've kept the logic where this will undelete an existing
import rather than create one from fresh, as I think that is beneficial
to the user (ie. it will still keep any linked scores on restore).
Also changes the realm filename to use `client` to match the ignore
rules in `OsuStorage`. Without doing this, migration will fail in an
indefinite mutex wait when attempting to delete the realm `.note` file.
For compatibility reasons, we quite often convert completely unmanaged
instances to `ILive`s so they fit the required parameters of a property
or method call. This ensures such cases will not cause any issues when
trying to interact with the underlying data.
Originally I had this allowing write operations, but that seems a bit
unsafe (when performing a write one would assume that the underlying
data is being persisted, whereas in this case it is not). We can change
this if the requirements change in the future, but I think throwing is
the safest bet for now.