Implement client conformance tests #711
Description
In #650, we added a basic harness for server conformance tests. That's an important milestone, as the server conformance tests are part of #675.
However, we should also (eventually) implement the client conformance examples from modelcontextprotocol/conformance (and add a script to run them). These are a little tricker, as there's more than just one client to implement. Also, we still have thin support for client-side oauth, which many of these tests cover.
I don't think this is super urgent: maybe wait for the client conformance tests to mature a bit.