HttpCtrl: set_stub_reply must not double-encode str/bytes bodies

        `status` [in] (int|string): HTTP status code for response that is used by server stub.

        `body` [in] (string|bytes): Response body that is used by server stub.

        `body` [in] (string|bytes|None or any JSON-serialisable Python object): Response body that is used by server stub.

            A `str` or `bytes` body is sent on the wire as-is — useful when the caller has already serialised

            JSON (e.g. via `Convert JSON To String`). Any other non-`None` value is run through `json.dumps()`

            so callers can also pass a Python `dict` / `list` directly. `None` sends an empty body.

        Example how to set stub to reply automatically to request `POST` `/api/v1/request` by status `200`.

            raise AssertionError(message_error)

        criteria = HttpStubCriteria(method=method, url=url)

        # Auto-serialise non-string bodies (e.g. Python dicts / lists) so callers

        # can pass either a Python data structure OR an already-serialised JSON

        # string. The previous unconditional `json.dumps(body)` double-encoded

        # string bodies — a stub body of `'[{"id":"X"}]'` (e.g. from

        # `Convert JSON To String`) was sent on the wire as

        # `'"[{\\"id\\":\\"X\\"}]"'` and parsed by the client as a string, not

        # an array.

        if not isinstance(body, (str, bytes)) and body is not None:

            body = json.dumps(body)

        response = Response(int(status), None, body, None, None)