zeroize: possible UB in `Zeroize` implementation for `Option<T>`

Originally filed by @jessa0 as https://github.com/iqlusioninc/crates/issues/782:

It seems the Zeroize implementation for Option<T> where T: Zeroize has language-level UB here:

https://github.com/RustCrypto/utils/blob/00b569b52b6dece2a8ae881f8e5a150a45ccc674/zeroize/src/lib.rs#L330

I believe, as a repr(Rust) enum, the memory layout and set of valid bit-patterns for Option is not defined, and that setting an enum's storage to an invalid bit-pattern while a reference to it exists, even if the value is never read, is instant language-level UB. The documentation for Option does mention guarantees for several special cases, but the None case still isn't defined for many of those cases, and the Zeroize implementation is more generic than that. Here's an example of a miri error in such a situation, that scottmcm came up with on URLO here.

Comienza en zeroize/src/lib.rs alrededor de la línea 330 y reproduce el comportamiento reportado usando el ejemplo enlazado de Rust Playground o Miri. Determina un enfoque sólido para la implementación de Option y verifica que el comportamiento resultante ya no desencadene el error de comportamiento indefinido reportado.