[rust][clippy] Enable -Dclippy::missing_safety_doc
[rust][clippy] Enable -Dclippy::missing_safety_doc

The roll out of this lint is tracked in fxbug.dev/98905.

Change-Id: I02a991f325773b0a7e49e0317dd07928bd14c38f
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/673522
Commit-Queue: David Koloski <b1df8881e735a70a3a455d7641f0502929cff7ad@google.com>
Reviewed-by: Tyler Mandry <23c76bee785596f2629881c8641bdc9aa64e7f7f@google.com>

google/zerocopy,google/zerocopy