Limit number of unique blockstates shown in anomalies to 500

[embeddedt]

My performance mod, ModernFix, provides an optional feature (disabled by default) that loads block & item models dynamically rather than all at startup. This drastically reduces game launch times and memory usage, and generally has little to no performance impact in-game. However, the BoP anomaly block presents a worst case scenario for the dynamic model loader, as it requests a random model (for any block state) on the main render thread roughly once a tick.

This PR attempts to mitigate the performance issue by limiting the number of unique blockstates shown by the anomaly to 500.

If this PR is accepted, and it's possible, a backport to 1.21.1 would be appreciated.

[Forstride]

I don't mind this, since the anomalies definitely need performance fixes across the board, but if it's going to be limited, I'd rather it only pull from vanilla blockstates if possible.