String responses are not passed to Response Deserializer

Hi,

I'm finding that if a route has a return type as string, the http content from the response is directly passed back instead of being first sent to the deserializer. It might be a saving but it's wrong in the case of custom deserializers.

I use restease exclusively with a protobuf-net serializer and this causes a rather unexpected gotcha as you can imagine. As i get the protobuf message directly interpreted as a string...

Let me know if that makes sense? Can dig around and make the PR if it helps. Thanks.

Start by locating the response-handling path and its deserializer selection logic in the RestEase codebase. Reproduce a route returning a string with a custom protobuf-net deserializer, then add a regression test showing that the response content is deserialized before it is returned.

Written by the indexing model from the issue text.