KcpTransport ServerUri returns empty host when machine name contains non-ASCII/invalid characters

[sxg15]

Summary

KcpTransport.ServerUri() builds a UriBuilder host from Dns.GetHostName(). If the computer name contains non-ASCII/invalid URI characters (e.g., Chinese), UriBuilder.Host ends up empty and the method returns kcp://:7777 (or throws), so the transport cannot provide a usable server URI.

Steps to Reproduce

1. Set the OS computer name to include a Chinese character (e.g., 测试PC).
2. Start a project using Mirror KCP.
3. Call Transport.activeTransport.ServerUri().

Expected

ServerUri() returns a valid URI with a usable host (e.g., punycode or a fallback like localhost).

Actual

Host is empty/invalid; URI becomes kcp://:port (or UriFormatException).

Notes

File: Mirror/Transports/KCP/KcpTransport.cs line ~191. Likely need to validate/IDN-encode the hostname and/or provide a fallback when invalid.