rust: zerocopy: import crate

This is a subset of the Rust `zerocopy` crate, version v0.8.50 (released
2026-05-31), licensed under "BSD-2-Clause OR Apache-2.0 OR MIT", from:

https://github.com/g

rust: zerocopy: import crate

This is a subset of the Rust `zerocopy` crate, version v0.8.50 (released
2026-05-31), licensed under "BSD-2-Clause OR Apache-2.0 OR MIT", from:

https://github.com/google/zerocopy/tree/v0.8.50

The files are copied as-is, with no modifications whatsoever (not even
adding the SPDX identifiers).

The `benches` folder is added (i.e. not just `src` like in other cases)
since the files there are included in the rendered documentation,
as well as the `rustdoc` CSS style file that is needed to make those
visually more understandable.

For copyright details, please see:

https://github.com/google/zerocopy/blob/v0.8.50/README.md?plain=1
https://github.com/google/zerocopy/blob/v0.8.50/LICENSE-BSD
https://github.com/google/zerocopy/blob/v0.8.50/LICENSE-APACHE
https://github.com/google/zerocopy/blob/v0.8.50/LICENSE-MIT

The next two patches modify these files as needed for use within the
kernel. This patch split allows reviewers to double-check the import
and to clearly see the differences introduced.

The following script may be used to verify the contents:

for path in $(cd rust/zerocopy/ && find . -type f); do
curl --silent --show-error --location \
https://github.com/google/zerocopy/raw/v0.8.50/$path \
| diff --unified rust/zerocopy/$path - && echo $path: OK
done

Cc: Joshua Liebow-Feeser <joshlf@google.com>
Cc: Jack Wrenn <jswrenn@google.com>
Link: https://patch.msgid.link/20260608141439.182634-9-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

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