Routes without x-method_name all get the same name (request_func) and replace each other #26

Follow-up from the adversarial review of #24. When a spec route has no x-method_name, mk_request_function keeps the default function name, so every such route registers as request_func and only the last survives (#24 now warns about the duplicate). Derive a name from operationId, or from method + path, when x-method_name is absent.