Derived route names that collide after sanitizing are not told apart #28

Follow-up from the adversarial review of #27. Routes named from operationId or method + path can collide once sanitized: /a-b, /a_b and /a/b all give get_a_b; /u/{id} and /u/id both give get_u_id; operationIds list-things and list_things; an operationId get_y against the path /y. Today each only warns and the last route wins, so api_pkg_files silently produces a package missing routes. Not a regression (before #27 they were all request_func). Options: suffix derived names deterministically (_2) in spec order, or raise in api_pkg_files when the warning fired. Recommendation: suffix only derived names (never an explicit x-method_name), and keep the warning. Also: a root path / is named after the bare method (get).