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/mod.rs

@@ -0,0 +1,13 @@
+pub mod codec;
+pub mod heartbeat;
+pub mod packet;
+pub mod polling;
+pub mod server;
+pub mod session;
+pub mod upgrade;
+pub mod websocket;
+pub mod webtransport;
+
+pub use packet::{HandshakeData, Packet, PacketData, PacketType};
+pub use server::{EngineConfig, EngineServer};
+pub use session::{SessionState, SessionStore, TransportType};