Callback that runs when the players health is updated

[Spearkiller]

Something like MC_PLAYER_HEALTH_UPDATE. While we have post damage callbacks, there’s a lot of other ways the players health can change. If we wanted to make a feature which did something when the players health changes, while not impossible and likely just needing to be ran/checked every frame, this would make it a heck of a lot easier/nicer, as it would be less code running every frame. Ideally this would fire not just when the player gains/loses health, but also whenever they get a health up, health down, broken heart, full heart reroll, etc — basically, anything that changes the players hp. This would have no return parameters as it is merely for checking the values, not changing them.