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

crates/polysafe_nifs/src/lib.rs

@@ -21,6 +21,7 @@
 //! Elixir side is responsible for tracking handle lifetimes via a
 //! GenServer or ETS table.
 
+#![forbid(unsafe_code)]
 use rustler::{Encoder, Env, NifResult, Term};
 
 mod atoms {