Content-Range header values are not validated and enforced

#### Environment details

* testbench version 0.45.0

#### Steps to reproduce

1. Retry conformance test [`http-7-[return-503-after-256K]-storage.objects.insert-50`](https://github.com/googleapis/conformance-tests/blob/e21bdd6b477cde487a6254cd1c70db04cba34c74/storage/v1/retry_tests.json#L254)
2. Full http log: https://gist.github.com/BenWhitehead/ae8a02958ff22e1e238057fed3732a15#file-http-log-L104
3. Notice on like 104 `Content-Range: bytes 262144-786431/524288`, the end of that range is larger than the specified total number of bytes.
4. Originally discovered while investigating https://github.com/googleapis/java-storage/issues/2770