feat(auth): add authentication protocol definitions and build configuration

- Add TokenClaims message for JWT payload structure with user id, issuer, timestamps, and scopes
- Implement IssueTokenRequest/Response for creating access and refresh tokens with TTL support
- Create RefreshTokenRequest/Response for token rotation functionality
- Define RevokeTokenRequest/Response with support for single token or user-wide revocation
- Add VerifyTokenRequest/Response for validating JWT tokens with detailed claims information
- Implement signing key distribution system with GetSigningKeysRequest/Response
- Create TokenService gRPC service with IssueToken, RefreshToken, RevokeToken, VerifyToken, and GetSigningKeys methods
- Add build.rs configuration to compile proto files using tonic_prost_build
- Include channel, channel_settings, member, and permission protocol definitions for IM services
- Generate Rust code bindings through pb/core.rs and pb/im.rs modules

engine/upgrade.rs

@@ -0,0 +1,53 @@
+use crate::engine::packet::Packet;
+use crate::engine::session::{SessionState, SessionStore, TransportType};
+
+pub async fn handle_upgrade_probe(
+    store: &SessionStore,
+    sid: &str,
+) -> Result<Packet, UpgradeError> {
+    let session = store.get(sid).ok_or(UpgradeError::SessionNotFound)?;
+    let mut session = session.write().await;
+
+    if session.state == SessionState::Closed {
+        return Err(UpgradeError::SessionClosed);
+    }
+
+    session.set_state(SessionState::Upgrading);
+    Ok(Packet::pong("probe"))
+}
+
+pub async fn handle_upgrade_complete(
+    store: &SessionStore,
+    sid: &str,
+    new_transport: TransportType,
+) -> Result<(), UpgradeError> {
+    let session = store.get(sid).ok_or(UpgradeError::SessionNotFound)?;
+    let mut session = session.write().await;
+
+    session.set_transport(new_transport);
+    session.set_state(SessionState::Open);
+
+    Ok(())
+}
+
+pub async fn send_noop_to_pending_polling(
+    store: &SessionStore,
+    sid: &str,
+) -> Result<(), UpgradeError> {
+    let session = store.get(sid).ok_or(UpgradeError::SessionNotFound)?;
+    let mut session = session.write().await;
+
+    session.buffer_packet(Packet::noop());
+
+    Ok(())
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum UpgradeError {
+    #[error("session not found")]
+    SessionNotFound,
+    #[error("session closed")]
+    SessionClosed,
+    #[error("invalid state for upgrade")]
+    InvalidState,
+}