refactor: 清理死代码和优化日志级别

- 删除未使用的函数和常量
  - create_public_key_message (rustdesk/connection)
  - decode_audio_packet, AudioPacketHeader (web/audio_ws)
  - io_error_to_hid_error, close_device, close_all_devices (hid)
  - shutdown_rx (rustdesk/mod)
  - CONNECT_TIMEOUT_MS, RESP_ERR_SEND_FAILED

- 调整日志级别
  - Session lagged: warn -> debug
  - 移除 H264 NAL trace 日志
  - 移除 Frame distribution lagged trace 日志
  - 移除 absolute mouse report trace 日志

- 优化 broadcast channel 缓冲区大小 8 -> 16

- 修复条件编译
  - static_files.rs: 添加 debug_assertions 条件

src/rustdesk/connection.rs

@@ -723,16 +723,6 @@ impl Connection {
         }
     }
 
-    /// Create public key message (for legacy compatibility)
-    fn create_public_key_message(&self) -> hbb::Message {
-        hbb::Message {
-            union: Some(message::Union::PublicKey(hbb::PublicKey {
-                asymmetric_value: self.keypair.public_key_bytes().to_vec(),
-                symmetric_value: vec![],
-            })),
-        }
-    }
-
     /// Handle peer's public key and negotiate session encryption
     /// After successful negotiation, send Hash message for password authentication
     async fn handle_peer_public_key(