Parse attribution simulation test options from input files

For now we only parse the delay mode, as the other options affect
simulation determinism. Once we allow noise seeds to be specified, we
will enable parsing of that option.

Bug: 1296186
Change-Id: Id199b5f3cca9100cc9034ae81eb0cbaa25385d47
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3457507
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Commit-Queue: Andrew Paseltiner <apaseltiner@chromium.org>
Cr-Commit-Position: refs/heads/main@{#970461}