This matches the implementation we have for `BeatmapInfo` and
`BeatmapSetInfo`. All comparisons of `OnlineID` should be done directly
using them (ie. how it's done in `ScoreModelDownloader`).
As it turns out, on some cultures, the "negative integer" sign is not
encoded using the U+002D HYPHEN-MINUS codepoint. For instance, Swedish
uses U+2212 MINUS SIGN instead. This was confusing the legacy decoder,
since it is correctly depending on the serialisation being
culture-independent.
To fix, ensure that the special "end replay" frame, as well as the
replay MD5 hash, are generated in a culture-invariant manner.
Thankfully the replay MD5 hash is currently being discarded in
`LegacyScoreDecoder`, so it changing in future scores should not have
any negative effect on lazer operation.
The recent changes related to adding support for working beatmap load
cancellation exposed a flaw in the beatmap difficulty cache. With the
way the difficulty computation logic was written, any error in the
calculation process (including beatmap load timeout, or cancellation)
would result in a 0.00 star rating being permanently cached in memory
for the given beatmap.
To resolve, change the difficulty cache's return type to nullable.
In failure scenarios, `null` is returned, rather than
`default(StarDifficulty)` as done previously.