World teleporting

[JunkyDeveloper]

Goal

Allow teleporting between worlds, which will also serve as the foundation for portals.
Only player teleportation is implemented — entity support (items, mobs) will come later.

Core Concept

Added a Vec and an AtomicBool to the server to queue and process dimension changes at the end of each tick. This avoids mid-tick world state inconsistencies.

In the Entity trait, a change_world function was added. Currently only Player has a real implementation — other entity types have a no-op stub.

The player teleportation goes through 5 phases:

1. Clean up old world (close containers, remove from tracking)
2. Reset player state (position, rotation, movement validation)
3. Send CRespawn + position packet to the client
4. Set portal cooldown (stub)
5. Add player to the new world

Also includes:

• portal/portal_shape.rs: portal frame detection matching vanilla's algorithm, used for future portal trigger support
• DimensionChangeRequest: two variants — Computed (direct teleport) and Portal (computes destination at processing time from a portal block position)

Testing

Added the command:
/steel tp <targets> <world id>
Accepts shorthand aliases (overworld, nether, end) or full identifiers (minecraft:overworld). Tab-completes all currently loaded worlds.

[github-actions]

This pull request has conflicts with the base branch "master". Please resolve those so we can test out your changes.

[github-actions]

Conflicts have been resolved! 🎉

[github-actions]

This pull request has conflicts with the base branch "master". Please resolve those so we can test out your changes.

[github-actions]

Conflicts have been resolved! 🎉