chore: add #![forbid(unsafe_code)] to safe Rust crates

Adds the forbid(unsafe_code) crate-level attribute to all Rust crates
that do not use unsafe code, hardening the safety guarantee at compile
time.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

impl/elixir/native/vsh_nif/src/lib.rs

@@ -3,6 +3,7 @@
 //!
 //! Exposes hardware-based secure erase functions to Elixir
 
+#![forbid(unsafe_code)]
 use rustler::Atom;
 
 // Import from vsh crate