GHSA-rcx8-48pc-v9q8 mail-internals use-after-free vulnerability in `vec_insert_bytes`

• crates.io mail-internals: >= 0.2.0, <= 0.2.3 (no fix yet)

Incorrect reallocation logic in the function `vec_insert_bytes` causes a use-after-free. This function does not have to be called directly to trigger the vulnerability because many methods on `EncodingWriter` call this function internally. The mail-\* suite is unmaintained and the upstream sources have been actively vandalised. A fixed `mail-internals-ng` (and `mail-headers-ng` and `mail-core-ng`) crate has been published which fixes this, and a dependency on another unsound crate.