Migrate to cargo_embargo. am: e5d8474b88

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/cast/+/2822151

Change-Id: I47e72773d3c5c24118bac50cf5f8cb189d434c66
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>