Add transfer packet backport (1.20.5 for 1.7.10)

[alppp]

backports 1.20.5 ClientboundTransferPacket to 1.7.10, allowing servers to seamlessly redirect players to another server:port without requiring BungeeCord/Velocity or other proxies. Migrated from Hodgepodge PR GTNewHorizons/Hodgepodge#833 per review feedback that a public API feature belongs in ServerUtilities.

• server sends host+port via ServerUtilities NetworkWrapper on the serverutilities channel
• client disconnects cleanly and reconnects to the target server
• /transfer [port] command (op level 3)
• TransferHelper.transfer() public API for programmatic use
• config: enableTransferPacket toggle, transferWhitelist for allowed hosts
• compatible with BungeeCord/Velocity/Bukkit proxies

wire format on the serverutilities channel:

Field	Value
Channel	serverutilities
Direction	Server to Client
Discriminator	0x0D

Wire Format

Uses ServerUtilities DataOut/DataIn serialization:

Field	Type	Description
host	String (DataOut.writeString)	Hostname or IP address (UTF-8, length-prefixed)
port	int (DataOut.writeInt)	Port number 1-65535

the client disconnect uses a deferred GuiTransferring screen to avoid a packet processing race in modded runTick -- updateController() can still dispatch stale packets after loadWorld(null) nulls the world, so the actual GuiConnecting is created in updateScreen() which runs after updateController in the tick cycle.

technically they could be done without this however it would be a hacky workaround for velocity, and would be a hit or miss. (higher chance of crash in dense populated gregtech machines area, and this just removes that chance)

An example can be seen here:

2026-04-14.20-43-53_compressed.mp4