Fixing tool response being lost

[julianstephen]

Issue #14

Part of the problem seems to be related to the response object returned by mcp tools.
E.g.,

In ExternalProcessorServicer->Process,

           if ...
           elif request.HasField("request_body") and request.request_body.body:
           ....
           elif request.HasField("response_body") and request.response_body.body:
            ...

Chunked responses from the mcp tool servers seems to skip the elif request.HasField("response_body") and request.response_body.body: block.

May need additional updates after some more testing. The test_slow servers seems not to be working still

[julianstephen]

Still has some problems with delayed responses. Can use this PR to discuss/update fixes.
I haven’t tested with internal plugins yet.