Introduce "Yodel" - a framework for testing things vaguely related to calls.
This is breaking up some work I did for transport test suites - we've got a nice way of spawning test-only promises and tracking them visually, and support for setting up an environment that can run as a test or a fuzzer. I'm making that piece a little more reusable, and then rebasing the transport test suite atop that infrastructure.
Closes#36635
COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/36635 from ctiller:transport-refs-6 843a9f4b7e
PiperOrigin-RevId: 637022756
621aa4e5ce