Function connect_channel_address_plan 

pub async fn connect_channel_address_plan(
    plan: &ChannelAddressPlan,
    push_cb: PushCallback,
    protocol_identity: BackendProtocolIdentity,
) -> Result<(BackendConn, String), FutuError>

Execute the common C++ Connector TCP stages for Platform and Broker.

Ref: FTNet/channel/impl/connector.cpp:224-266.