feat: upgrade to donglora-client 0.2, fix org URLs, publish-ready

- Upgrade donglora-client from 0.1 (monorepo path dep) to 0.2 (crates.io)
- Import wire-level constants from donglora_client::protocol::*
- Fix repository URL to github.com/donglora/mux-rs
- Add homepage, rust-version, exclude to Cargo.toml
- Fix README (remove monorepo paths, add install instructions)
- Allow clippy unwrap in test module

src/session.rs

@@ -30,11 +30,7 @@ impl ClientSession {
     pub fn new() -> (Self, mpsc::Receiver<Vec<u8>>) {
         let id = NEXT_CLIENT_ID.fetch_add(1, Ordering::Relaxed);
         let (tx, rx) = mpsc::channel(SEND_QUEUE_CAP);
-        let session = Self {
-            id,
-            rx_interested: false,
-            tx,
-        };
+        let session = Self { id, rx_interested: false, tx };
         (session, rx)
     }