Function connect 

pub async fn connect(
    stream: BoxStream,
    target: &Target,
    username: Option<&str>,
    password: Option<&str>,
) -> Result<BoxStream>

Perform a SOCKS5 CONNECT handshake on an already-connected stream.

Supports:

• No-auth (method 0x00)
• Username/password auth (method 0x02, RFC 1929)
• IPv4, IPv6, and hostname targets

Errors

Returns an error if the handshake fails, auth is rejected, or the proxy returns a non-success reply.