feat(usockets): optimize high concurrency support up to 10,000+ connections

- Increase uSockets listen() backlog from 512 to 16384 in bsd.c
- Add high concurrency test suite (5000-10000 concurrent connections)
- Add HIGH_CONCURRENCY.md documentation with optimization guide
- Add usockets/build.sh script for rebuilding uSockets library
- Update README with latest benchmark results

Performance (macOS M3 Max):
- 5,000 concurrent: 81,524 RPS, 100% success
- 10,000 concurrent: 24,198 RPS, 100% success

System requirements:
- kern.ipc.somaxconn >= 8192
- ulimit -n 65535

usockets/build.sh

@@ -0,0 +1,55 @@
+#!/bin/bash
+# uSockets 编译脚本
+# 用于重新编译 libusockets_full.a
+
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+USOCKETS_DIR="/tmp/uSockets"
+
+echo "=== uSockets 编译脚本 ==="
+
+# 检查是否有 uSockets 源码
+if [ ! -d "$USOCKETS_DIR" ]; then
+    echo "克隆 uSockets..."
+    git clone --depth 1 https://github.com/uNetworking/uSockets.git "$USOCKETS_DIR"
+fi
+
+# 应用 backlog 修改
+echo "应用 backlog=16384 修改..."
+if [ -f "$SCRIPT_DIR/src/bsd.c" ]; then
+    cp "$SCRIPT_DIR/src/bsd.c" "$USOCKETS_DIR/src/bsd.c"
+else
+    # 如果没有本地修改的源码，直接修改
+    sed -i.bak 's/listen(listenFd, 512)/listen(listenFd, 16384)/g' "$USOCKETS_DIR/src/bsd.c"
+fi
+
+# 编译
+echo "编译 uSockets..."
+cd "$USOCKETS_DIR"
+make clean
+
+# 根据系统选择编译参数
+if [[ "$OSTYPE" == "darwin"* ]]; then
+    # macOS
+    if [[ $(uname -m) == "arm64" ]]; then
+        # Apple Silicon
+        WITH_LIBUV=1 CFLAGS="-I/opt/homebrew/include" make
+    else
+        # Intel Mac
+        WITH_LIBUV=1 CFLAGS="-I/usr/local/include" make
+    fi
+else
+    # Linux
+    WITH_LIBUV=1 make
+fi
+
+# 复制到 v-hono
+echo "复制库文件..."
+cp "$USOCKETS_DIR/uSockets.a" "$SCRIPT_DIR/../lib/libusockets_full.a"
+
+echo "=== 编译完成 ==="
+echo "库文件: $SCRIPT_DIR/../lib/libusockets_full.a"
+echo ""
+echo "重新编译 v-hono 应用:"
+echo "  v -enable-globals -prod -o your_app your_app.v"