Hysteria2: support Gecko obfuscation from apernet/hysteria v2.9.2

[luvkult]

apernet/hysteria added Gecko obfuscation in v2.9.2. It fragments QUIC long-header packets into 2-8 random-sized chunks with random padding, then sends each fragment through a Salamander wrap. Short-header packets pass through plain Salamander. Spec is in PROTOCOL.md, config keys are obfs.type: gecko + gecko.password / minPacketSize / maxPacketSize.

sing-box currently accepts only obfs.type: salamander for hysteria2. Subscription URIs carrying ?obfs=gecko&obfs-password=... are silently dropped from imported profiles (Karing 1.2.19.2208 on Android, kernel sing-box 1.13.x — entry vanishes with no parse error in core log).

Repro

1. Server: apernet/hysteria v2.9.2, obfs.type: gecko, password X.
2. Client URI: hysteria2://pw@host:443/?sni=host&alpn=h3&obfs=gecko&obfs-password=X#NL.
3. Import via subscription. Profile list shows no NL entry; no error surfaced to the user.

Expected

Either parse obfs=gecko and apply the Gecko transform on the QUIC layer, or surface an explicit "unsupported obfs type" error so it doesn't disappear silently.

Refs

• Release: https://github.com/apernet/hysteria/releases/tag/app/v2.9.2
• Config: https://v2.hysteria.network/docs/advanced/Full-Server-Config/
• Spec: https://github.com/apernet/hysteria/blob/master/PROTOCOL.md (Gecko section)

Use case

Salamander wraps QUIC into random UDP, but Initial packet sizes still cluster around 1200 bytes which is observable to statistical DPI. Gecko randomises that distribution.

Happy to test a patch on a real chain (3 nodes, ~200 active clients).

[luvkult]

Thanks for the quick implementation in commit 56a... (1.14.0-alpha.26 release today). Closing as resolved — will pick it up when 1.14.0 stable lands.