Improve Fragment handling in JSON::Encoding

Author: byroot

actionpack/profile-20250213-085143-11604.vernier.json

@@ -85,7 +85,6 @@ def encode(value)
           # to +object.as_json+, not any of this method's recursive +#as_json+
           # calls.
           def jsonify(value)
-            return value if value.class.name == "JSON::Fragment"
             case value
             when String, Integer, Symbol, nil, true, false
               value
@@ -101,7 +100,11 @@ def jsonify(value)
             when Array
               value.map { |v| jsonify(v) }
             else
-              jsonify value.as_json
+              if defined?(::JSON::Fragment) && ::JSON::Fragment === value
+                value
+              else
+                jsonify value.as_json
+              end
             end
           end