Remove redundant string constructors

Author: chusitoo

ext/src/http/client/curl/http_client_curl.cc

@@ -134,7 +134,7 @@ void Session::SendRequest(
     std::shared_ptr<opentelemetry::ext::http::client::EventHandler> callback) noexcept
 {
   is_session_active_.store(true, std::memory_order_release);
-  std::string url       = host_ + std::string(http_request_->uri_);
+  const auto& url       = host_ + http_request_->uri_;
   auto callback_ptr     = callback.get();
   bool reuse_connection = false;
 

ext/src/http/client/curl/http_operation_curl.cc

@@ -301,9 +301,7 @@ HttpOperation::HttpOperation(opentelemetry::ext::http::client::Method method,
   {
     for (auto &kv : this->request_headers_)
     {
-      std::string header = std::string(kv.first);
-      header += ": ";
-      header += std::string(kv.second);
+      const auto header = std::string(kv.first).append(": ").append(kv.second);
       curl_resource_.headers_chunk =
           curl_slist_append(curl_resource_.headers_chunk, header.c_str());
     }