Update our vendored copy of `zerocopy` (and `zerocopy-derive`) to v0.8.54.

It is a very small delta from v0.8.52, and most importantly it resolves
the unexpected lack of inlining [1] which triggered a modpost error
under `CONFIG_CC_OPTIMIZE_FOR_SIZE=y` reported by Alexandre using Gary's
suggestion [2]:

    ERROR: modpost: "_RNvMNtCs5wX7wwEUCR9_8zerocopy6layoutNtB2_8SizeInfo24try_to_nonzero_elem_size" [drivers/gpu/nova-core.ko] undefined!
    ERROR: modpost: "_RNvNtCs5wX7wwEUCR9_8zerocopy4util18padding_needed_for" [drivers/gpu/nova-core.ko] undefined!

It also resolves `most_traits` being unexpectedly documented [3] that I
reported and adds a missing SPDX license identifier [4] that I requested
to match the kernel version.

The following script may be used to check for the remaining differences:

    for path in $(cd rust/zerocopy-derive/ && find . -type f ! -name README.md); do
        curl --silent --show-error --location \
            https://github.com/google/zerocopy/raw/v0.8.54/zerocopy/zerocopy-derive/src/$path |
            git diff --no-index - rust/zerocopy-derive/$path &&
            echo $path: OK
    done

    for path in $(cd rust/zerocopy/ && find . -type f ! -name README.md); do
        curl --silent --show-error --location \
            https://github.com/google/zerocopy/raw/v0.8.54/zerocopy/$path |
            git diff --no-index - rust/zerocopy/$path &&
            echo $path: OK
    done

Cc: Joshua Liebow-Feeser <joshlf@google.com>
Cc: Jack Wrenn <jswrenn@google.com>
Reported-by: Alexandre Courbot <acourbot@nvidia.com>
Closes: https://lore.kernel.org/rust-for-linux/20260708-zerocopy-export-v1-1-2bfc355853c6@nvidia.com/ [1]
Suggested-by: Gary Guo <gary@garyguo.net>
Link: https://lore.kernel.org/rust-for-linux/DJT6235B3DOV.222XR5O6VHG4M@garyguo.net/ [2]
Link: https://github.com/google/zerocopy/issues/3466 [3]
Link: https://github.com/google/zerocopy/issues/3457 [4]
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Tested-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260709211311.142544-1-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Update our vendored copy of `zerocopy` (and `zerocopy-derive`) to v0.8.52.

Most SPDX identifiers have been added upstream at our request [1]
(without parentheses -- supporting them is an issue on the kernel side,
but it does already reduce our differences). The CSS one for `rustdoc`
was added too [2], but will be picked up in a later version.

For `zerocopy`, enable `--cfg no_fp_fmt_parse`, which was added at our
request to avoid our local workaround [3]. This means one less difference,
thus indicate so in our `README.md`.

For `zerocopy-derive`, enable `--cfg zerocopy_unstable_linux`. This
allows us to use `#[derive(zerocopy_derive::most_traits)]`, a new feature
upstream added for us [4]. We noticed a minor doc render bug [5], which
will be fixed for a future version too.

The following script may be used to check for the remaining differences:

    for path in $(cd rust/zerocopy-derive/ && find . -type f ! -name README.md); do
        curl --silent --show-error --location \
            https://github.com/google/zerocopy/raw/v0.8.52/zerocopy/zerocopy-derive/src/$path |
            git diff --no-index - rust/zerocopy-derive/$path &&
            echo $path: OK
    done

    for path in $(cd rust/zerocopy/ && find . -type f ! -name README.md); do
        curl --silent --show-error --location \
            https://github.com/google/zerocopy/raw/v0.8.52/zerocopy/$path |
            git diff --no-index - rust/zerocopy/$path &&
            echo $path: OK
    done

Cc: Joshua Liebow-Feeser <joshlf@google.com>
Cc: Jack Wrenn <jswrenn@google.com>
Link: https://github.com/google/zerocopy/issues/3428 [1]
Link: https://github.com/google/zerocopy/issues/3457 [2]
Link: https://github.com/google/zerocopy/issues/3426 [3]
Link: https://github.com/google/zerocopy/pull/3416 [4]
Link: https://github.com/google/zerocopy/issues/3466 [5]
Acked-by: Nicolas Schier <n.schier@fritz.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20260625231919.692444-1-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Originally, when the Rust upstream `alloc` standard library crate was
vendored, the SPDX License Identifiers were added to every file so that
the license on those was clear. The same happened with the vendoring of
`proc_macro2`, `quote` and `syn`. Please see:

  commit 057b8d257107 ("rust: adapt `alloc` crate to the kernel")
  commit 69942c0a8965 ("rust: syn: add SPDX License Identifiers")
  commit ddfa1b279d08 ("rust: quote: add SPDX License Identifiers")
  commit a9acfceb9614 ("rust: proc-macro2: add SPDX License Identifiers")

Thus do the same for the `zerocopy-derive` crate.

This makes `scripts/spdxcheck.py` pass: use parentheses like commit
06e9bfc1e57d ("ionic: make spdxcheck.py happy") did since we have two
`OR` operators in the expression (three licenses).

Finally, as requested, I filed an issue [1] with upstream about it.

Cc: Joshua Liebow-Feeser <joshlf@google.com>
Cc: Jack Wrenn <jswrenn@google.com>
Link: https://github.com/google/zerocopy/issues/3428 [1]
Link: https://patch.msgid.link/20260608141439.182634-15-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

This is a subset of the Rust `zerocopy-derive` 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/zerocopy-derive/src

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

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

Cc: Joshua Liebow-Feeser <joshlf@google.com>
Cc: Jack Wrenn <jswrenn@google.com>
Link: https://patch.msgid.link/20260608141439.182634-14-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>