merge(core/layers): layers system into main

[fIyingPhoenix]

Description

Implements a layer system that allows multiple layers to spawn within the same map. By default, each layer supports up to 400 players, but the system is dynamic, meaning a map can handle additional layers depending on the number of active players.

Layers can only be changed while in a group, ensuring that all group members stay in the same layer and preventing abuse of the system.

The layer system has been tested with 2 layers without any issues, though testing was only done with 4 players, so more extensive testing is still needed. Layer switching is almost unnoticeable, and each layer runs on its own thread.

Additional configuration options have been added to worldserver.conf, allowing modification of:

• Maximum players per layer
• Layer change cooldown
• Minimum number of players required before a new layer is created

Type of change

• C++ fix / feature

Testing

• Compiles without warnings
• Server boots successfully
• Tested in-game

Checklist

• One fix per PR — not mixed with unrelated changes
• SQL files follow the YYYY_MM_DD_NN_database.sql naming scheme
• No debug code or leftover TODOs