fix: downgrade undici to v6 and add SOCKS proxy support for undici dispatcher path

[Copilot]

A prior commit ("support socks proxy") accidentally bumped undici from ^6.24.1 to ^7.23.0, breaking Node.js 18 compatibility (File is not defined). undici v7 requires Node.js ≥ 20.18.1.

Changes

• package.json: Revert undici to ^6.24.1; add socks (^2.8.4) as a direct dependency
• src/config.ts:
  • Import buildConnector from undici and SocksClient from socks
  • Extend DispatcherOptions with a 'socks' variant ({ type: 'socks'; uri: string; requestTls: tls.ConnectionOptions })
  • In createDispatcherOptions, return { type: 'socks' } for SOCKS proxy URLs instead of throwing
  • Add createSocksConnector() — creates an undici-compatible connector that tunnels connections through the SOCKS proxy using SocksClient.createConnection, with TLS upgrade for https: targets
  • In createDispatcher, handle type: 'socks' by creating a UndiciAgent with the custom socks connector
• src/config_test.ts: Restore socks proxy test to verify a UndiciAgent is set as the dispatcher and createDispatcherOptions returns { type: 'socks', uri: 'socks5://...' }

SOCKS proxy now works on both the createDispatcher path (undici/fetch) and the legacy createAgent path (WebSocket / applyToHTTPSOptions).

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[brendandburns]

@copilot update this to use SocksProxyAgent when the proxy type is socks and restore the test for socks.

[Copilot]

@copilot update this to use SocksProxyAgent when the proxy type is socks and restore the test for socks.

Done in 2152769. The createDispatcher path now supports SOCKS proxies via a custom undici Agent connector (createSocksConnector) that uses SocksClient.createConnection to tunnel connections through the SOCKS proxy, with TLS upgrade for https: targets. Added socks as a direct dependency and a new 'socks' variant to DispatcherOptions. The test is restored to verify UndiciAgent is set as the dispatcher and createDispatcherOptions returns { type: 'socks', uri: 'socks5://example:1187' }.