websocket/stream: Fix unexpected EOF on Poll::Pending state poisoning (#327)

This PR updates the following dependencies:
- tokio tungstenite
- URL crate to facilitate the new tungstenite version

The tokio tungstenite update changed the API of webscoket messages,
which motivated the following changes:
- When`poll_ready` or `poll_flush` returned `Poll::Pending`, the
websocket state would forever remain poisoned.
- This has the side effect of returning `UnexpectedEof` on consecutive
calls, which led to the connection being terminated
- The state machine of the websocket is simplified to just 3 states
- Writer buffer and pointer are merged under one BytesMut instance
- `poll_read` implementation is simplified as well to make the code more
readable

---------

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

Author: lexnv

Cargo.lock

@@ -39,14 +39,14 @@ socket2 = { version = "0.5.8", features = ["all"] }
 str0m = { version = "0.6.2", optional = true }
 thiserror = "2.0.11"
 tokio-stream = "0.1.12"
-tokio-tungstenite = { version = "0.20.0", features = ["rustls-tls-native-roots"], optional = true }
+tokio-tungstenite = { version = "0.26.1", features = ["rustls-tls-native-roots", "url"], optional = true }
 tokio-util = { version = "0.7.11", features = ["compat", "io", "codec"] }
 tokio = { version = "1.26.0", features = ["rt", "net", "io-util", "time", "macros", "sync", "parking_lot"] }
 tracing = { version = "0.1.40", features = ["log"] }
 hickory-resolver = "0.24.2"
 uint = "0.10.0"
 unsigned-varint = { version = "0.8.0", features = ["codec"] }
-url = "2.4.0"
+url = "2.5.4"
 webpki = { version = "0.22.4", optional = true }
 x25519-dalek = "2.0.1"
 x509-parser = "0.17.0"