Use coroutines for Blinky::Blink loop Change-Id: If311d14f5e29d67fd528fef8afb2753f45342f03 Reviewed-on: https://pigweed-internal-review.git.corp.google.com/c/pigweed/showcase/rp2/+/72297 Reviewed-by: Alexei Frolov <frolv@google.com> Commit-Queue: Taylor Cramer <cramertj@google.com>