fix(libhttp,dnfs2): HttpClient 新增超时接口，dnfs2 启用配置超时

修复 dnfs2 审计 L-3（P2-N5）：

libhttp HttpClient 硬编码 CURLOPT_TIMEOUT=30L/CONNECTTIMEOUT=10L，
dnfs2 的 gateway_timeout/review_timeout 配置加载后从未使用，实际超时恒为 30s。

修复：
- libhttp HttpClient 新增 set_timeout/set_connect_timeout 接口
  （默认 30s/10s，向后兼容 gateway/core）
- request_stream_sync 使用成员变量替代硬编码值
- dnfs2 decode_token 设置 gateway_timeout
- dnfs2 review_content 设置 review_timeout

安全评级 A- → A，已知限制 6→5 项。

libhttp/src/HttpClient.cpp

@@ -42,6 +42,22 @@ size_t HttpClient::get_max_response_size() const {
     return max_response_size_;
 }
 
+void HttpClient::set_timeout(long seconds) {
+    timeout_ = seconds;
+}
+
+long HttpClient::get_timeout() const {
+    return timeout_;
+}
+
+void HttpClient::set_connect_timeout(long seconds) {
+    connect_timeout_ = seconds;
+}
+
+long HttpClient::get_connect_timeout() const {
+    return connect_timeout_;
+}
+
 void HttpClient::set_header(const std::string& header) {
     headers_ = curl_slist_append(headers_, header.c_str());
 }
@@ -89,8 +105,8 @@ void HttpClient::request_stream_sync(
     curl_easy_setopt(curl_, CURLOPT_WRITEFUNCTION, write_callback);
     curl_easy_setopt(curl_, CURLOPT_WRITEDATA, &write_ctx);
 
-    curl_easy_setopt(curl_, CURLOPT_TIMEOUT, 30L);
-    curl_easy_setopt(curl_, CURLOPT_CONNECTTIMEOUT, 10L);
+    curl_easy_setopt(curl_, CURLOPT_TIMEOUT, timeout_);
+    curl_easy_setopt(curl_, CURLOPT_CONNECTTIMEOUT, connect_timeout_);
 
     CURLcode res = curl_easy_perform(curl_);