Return errors from subcommands

This pulls in `anyhow` and updates subcommand implementations to return
results which propagate up to main.

Change-Id: Idd360e03c1adf8960c09a2690bf5e0753ac3e464
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/qg/+/119870
Commit-Queue: Alexei Frolov <frolv@google.com>
Reviewed-by: Erik Gilling <konkers@google.com>