[Bug Report] World metrics don't work on Folia

[sladkoff]

• ⚒️ Metrics mc_entities_total, mc_villagers_total will need to be re-implemented to use the new RegionScheduler class. It is no longer possible to call World#getEntities from the main thread.
  • If we use the regionised scheduling, we can add the label region to the metric and the total entity counts can be aggregated by Prometheus/Grafana.
  • It should also be possible to use an event-based approach (see Improve performance of chunk loaded metric and offline player count  #226). Basically, we can subscribe to entity load/unload events and count entities that way.