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/webrtc/video_track.rs

@@ -376,7 +376,6 @@ impl UniversalVideoTrack {
                 _ => {}
             }
 
-            trace!("H264 NAL: type={} size={}", nal_type, nal.data.len());
             nals.push(nal.data.freeze());
         }