Closes https://github.com/ppy/osu/issues/18468.
This doesn't stop the tutorial from downloading a second time, but at
least displays the correct status afterwards. Avoiding the download is a
bit more involved and requires a change to the flow. Probably not worth
it just yet.
To test, recommend switching to production environment, as dev server
doesn't have correct metadata for tutorial resulting in weirdness.
Will still keep the override in `ClockBackedTestWorkingBeatmap` because
it still relies on a local track store and will fail the moment it uses
a non-virtual track.
A lot of tests are using test resources that populate the length field,
but do not populate hitobjects. The general expectation is that
components should be using the cached length in cases where hitobjects
are not relevant, but `GetVirtualTrack` was doing its own local
calculation.
This could cause tests to fail due to `MusicController` changing track
in the background.