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.
After the recent changes introducing cancellation support to
`WorkingBeatmap`, it turned out that if the cancellation support was
used, `GetPlayableBeatmap()` would raise timeout exceptions rather than
the expected `OperationCanceledException`.
To that end, split off a separate overload for the typical usage, that
catches `OperationCanceledException` and converts them to beatmap load
timeout exceptions, and use normal `OperationCanceledException`s in the
overload that requires a cancellation token to work.