Add copying utility methods to Arena

tests/test_server.cpp

@@ -8,24 +8,14 @@
 #include <string_view>
 #include <thread>
 
-// Helper to copy a string into arena memory
-static std::string_view arena_copy_string(std::string_view str, Arena &arena) {
-  if (str.empty()) {
-    return std::string_view{};
-  }
-  char *copied = arena.allocate<char>(str.size());
-  std::memcpy(copied, str.data(), str.size());
-  return std::string_view(copied, str.size());
-}
-
 struct EchoHandler : ConnectionHandler {
   Arena arena;
   std::span<std::string_view> reply;
   WeakRef<MessageSender> wconn;
   std::latch done{1};
   void on_data_arrived(std::string_view data, Connection &conn) override {
-    reply = std::span{arena.allocate<std::string_view>(1), 1};
-    reply[0] = arena_copy_string(data, arena);
+    reply = arena.allocate_span<std::string_view>(1);
+    reply[0] = arena.copy_string(data);
     wconn = conn.get_weak_ref();
     CHECK(wconn.lock());
     done.count_down();