add CTOS_EXTERNAL_ADDRESS

[purerosefallen]

/*
* CTOS_ExternalAddress
* uint32_t real_ip; (IPv4 address)
* uint16_t hostname[256]; (UTF-16 string)
*/

Identical to the Host and X-Forwarded-For header in HTTP.

Not used in YGOPro itself, but useful in some reverse proxy or something like nginx or bungeecord to route YGOPro traffic.

[Copilot]

Pull Request Overview

This PR introduces a new message type, CTOS_EXTERNAL_ADDRESS, for routing YGOPro traffic through reverse proxies. Key changes include adding CTOS_EXTERNAL_ADDRESS definitions in network headers, a new case in netserver packet handling, and client logic for sending the external address data.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
gframe/network.h	Added CTOS_EXTERNAL_ADDRESS structure documentation and LEN_HOSTNAME constant.
gframe/netserver.cpp	Added a case for CTOS_EXTERNAL_ADDRESS with placeholder (commented) implementation.
gframe/duelclient.cpp	Implemented sending of CTOS_EXTERNAL_ADDRESS data using manual buffer construction.

[purerosefallen]

for ref:
https://code.moenext.com/mycard/ygopro-router/
https://code.moenext.com/mycard/srvpro/-/commit/c653047619f9f54212567c8a2ba6fc7b8673cc9c