Provide grpc clients #15
Description
If we had an http/2 client library that supported trailers, we could add gRPC clients.
Unfortunately, httpcore (the basis for httpx, see #10) does not have trailer support, and the maintainers of that library described http/2 trailers as an "unwin" (https://github.com/encode/httpcore/pull/1012#issuecomment-2862255448)` so it might not ever arrive.
hyper-h2 seems to support trailers, but is such a low-level client library that users will likely be unfamiliar with it.