GHSA-74R5-G7VC-J2V2 zerovec-derive incorrectly uses `#[repr(packed)]`

The affected versions make unsafe memory accesses under the assumption that reprpacked has a guaranteed field order. The Rust specification does not guarantee this, and https://github.com/rust-lang/rust/pull/125360 1.80.0-beta starts reordering fields of reprpacked structs, leading to illegal...