This implements an RPC service that streams pw_unit_test events, as well
as a unit test main that initializes a server with the test service
registered and an HDLC serial channel.
Change-Id: I6c66f2216c54d82aa70c351d7d3d99d9a5c173de
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/23901
Commit-Queue: Alexei Frolov <frolv@google.com>
Reviewed-by: Keir Mierle <keir@google.com>
