Add a benchmark for punycode -> unpunycode round trip.

Author: Dan Lecocq

bench.cpp

@@ -44,7 +44,8 @@ int main(int argc, char* argv[]) {
     size_t runs = 5;
 
     Url::Url base_url(base);
-    std::string full = Url::Url(relative).relative_to(base_url).str();
+    Url::Url full_url = Url::Url(relative).relative_to(base_url);
+    std::string full = full_url.str();
 
     bench("parse", count, runs, [full]() {
         Url::Url parsed(full);
@@ -65,4 +66,8 @@ int main(int argc, char* argv[]) {
     bench("parse + punycode", count, runs, [full]() {
         Url::Url(full).punycode();
     });
+
+    bench("punycode + unpunycode", count, runs, [full_url]() mutable {
+        full_url.punycode().unpunycode();
+    });
 }