Improve some server system performance

There is one part of this change that affects game behavior/assumptions. Currently, the game allows chunks outside of the map to remain loaded; with this MR, chunks outside of the map bounds exist purely client side. This is done for a number of optimization-related reasons. A consequence of this is that currently, entities that are not anchored in some way (e.g. pets) will disappear when leaving the map bounds. However, if this behavior is desired in the future, there are fast solutions available for keeping out of bounds entities within a player's view distance around. Adding out of bounds chunks would be a bit more of a problem, however; this is not currently something we've wanted to use for anything, and IMO we should solve such issues in better ways, but I'm mentioning it so that people know who to yell at if we have a critical need for such chunks to be held in memory on the server.

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• Migrations have been added if applicable
• Significant changes of this merge request have been added to the changelog.