Function unsupported_version_response 

pub fn unsupported_version_response(
    unstable: UnstableApiVersions,
) -> ApiVersionsResponse

Kafka’s ApiVersionsRequest.getErrorResponse for UNSUPPORTED_VERSION (KIP-511).

It is error 35 and exactly one api_keys entry, the range of ApiVersions itself (ApiVersionsResponse.toApiVersion(API_VERSIONS)), which the client reads to pick the version it retries with.

Every listener, broker or controller, answers with these bytes in a v0 body.