Make BossMob.isBossFight() return accurate values when called on the client

[Neko2n]

Currently, isBossFight returns data that's only updated on the server-side, so trying to get whether a boss is active or not on the client will return old data. The data only updates once the player dies, rejoins, or switches dimensions, at which point they're sent the updated data from the server and the method will return an accurate value.

My use case for this feature is that I'm trying to make a mod that plays boss music for Aether's bosses. I want the mod to be fully client-sided so people who have the mod installed can join servers that don't, but without accurate data I can't make the boss music only play when the bosses are actually active.

I posted a similar issue on the Aether github, although that request was significantly less reasonable... I'm new to modding and making this issue seems to be my only solution atm. If there's another way around this please let me know and I'll be happy to close the issue.