feat(core): implement RawFramingInterface accept/recv/send with first-frame auth

Implement RawFramingSession with tokio::io::split for read/write halves,
BufReader/BufWriter for buffered I/O, and decode_with_remainder for
partial frame reassembly. Add first-frame authentication via
IdentityProvider::resolve_from_token(). Add RawFramingConfig.auth
field for IdentityProvider reference. Update SshInterface test for
new RawFramingConfig shape.

crates/alknet-core/src/interface/ssh.rs

@@ -734,7 +734,11 @@ mod tests {
         let (_client, server) = tokio::io::duplex(1024);
         let stream: Box<dyn TransportStream> = Box::new(server);
 
-        let raw_config = StreamInterfaceConfig::RawFraming(crate::interface::RawFramingConfig {});
+        let raw_config = StreamInterfaceConfig::RawFraming(crate::interface::RawFramingConfig {
+            auth: Arc::new(crate::auth::ConfigIdentityProvider::new(Arc::new(
+                ArcSwap::new(Arc::new(DynamicConfig::default())),
+            ))),
+        });
         let result = iface.accept(stream, &raw_config).await;
         assert!(result.is_err());
     }