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

build/cross/Dockerfile.x86_64

@@ -3,6 +3,10 @@
 
 FROM debian:12
 
+# Set Rustup mirrors (Aliyun)
+ENV RUSTUP_UPDATE_ROOT=https://mirrors.aliyun.com/rustup/rustup \
+    RUSTUP_DIST_SERVER=https://mirrors.aliyun.com/rustup
+
 # Install Rust toolchain
 RUN apt-get update && apt-get install -y --no-install-recommends \
     curl \
@@ -22,6 +26,9 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     git \
     libclang-dev \
     llvm \
+    protobuf-compiler \
+    libssl-dev \
+    mold \
     # Core system libraries
     libasound2-dev \
     libv4l-dev \
@@ -55,3 +62,6 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 
 # Add Rust target
 RUN rustup target add x86_64-unknown-linux-gnu
+
+# Configure mold as the linker
+ENV RUSTFLAGS="-C link-arg=-fuse-ld=mold"