Remove std::copy usage. (#3550)

include/fmt/format.h

@@ -2896,7 +2896,7 @@ class bigint {
     auto size = other.bigits_.size();
     bigits_.resize(size);
     auto data = other.bigits_.data();
-    std::copy(data, data + size, bigits_.data());
+    copy_str<bigit>(data, data + size, bigits_.data());
     exp_ = other.exp_;
   }