Refactor net::PortForwarder to reduce handle fn

This change reduces the code size of `handle` fn inside `PortForwarder`
by moving the code inside it to new functions `handle_plaintext`,
`handle_encrypt` and `handle_decrypt`. This makes the code more
readable and easier to understand. Also, common code between
`handle_encrypt` and `handle_decrypt` is moved to two new functions
`initiator_handshake` and `responder_handshake`. All the changes
are made without changing the functionality of the code and as such
should not break anything and should be compatible with the previous
commit.

src/cli.rs

@@ -274,7 +274,7 @@ pub enum ConsumerCommands {
     },
     /// Stop device screen mirroring for a device.
     /// Note: This doesn't work if the Consumer and Supplier are on the same machine.
-    ///       see: https://github.com/mobi-nex/adborc/issues/16 for more information. 
+    ///       see: https://github.com/mobi-nex/adborc/issues/16 for more information.
     StopScrcpy {
         /// `device_id` of the device to stop scrcpy for.
         #[clap(value_parser)]

src/lib.rs

@@ -65,7 +65,6 @@
 //!     net::TCPClient,
 //!     util::SysStateDefaultConfig
 //! };
-//! # use serde_json;
 //!
 //! // start the system in a separate thread.
 //! thread::spawn(|| SysState::start_system().unwrap());