Ensure no DurableOrchestrationClient methods fail to decode mesages

When using aiohttp, the library will, by default, validate that the encoding of a server message matches its format but, with Azure Functions and many other services, the message encoding metadata is often not up to data. This mismatch yields a `mimetype encoding` runtime exception that we've already had to fix in multiple places.

We should create a robust tester to ensure these kinds of error no longer take place in our codebase.