refactor: reorganize API and WebSocket modules

Split client, endpoint, and WebSocket implementations into domain-focused modules while preserving the public API.\n\nImprove crate and API documentation to describe responsibilities, authentication boundaries, and response compatibility.

src/websocket/mod.rs

@@ -0,0 +1,20 @@
+//! Bilibili 直播 WebSocket 协议支持。
+//!
+//! 本模块将传输数据包、连接生命周期和业务命令分离：二进制数据包支持压缩载荷，
+//! 连接实现认证、心跳与事件读取，业务命令则转换为强类型事件。
+//!
+//! [LiveWebSocket] 是面向在线消费的入口；[decode_events] 可用于离线重放已捕获的原始帧。
+
+mod command;
+mod connection;
+mod packet;
+
+pub use command::*;
+pub use connection::LiveWebSocket;
+pub use packet::{decode_events, decode_packets, LiveEvent, Packet};
+
+#[cfg(test)]
+use packet::{encode_packet, events_from_packets};
+
+#[cfg(test)]
+mod tests;