Claude review: rust: types: add `ForLt` trait for higher-ranked lifetime support

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

The ForLt infrastructure by Gary Guo. The trait:

```rust
pub unsafe trait ForLt {
    type Of<'a>: 'a;
    fn cast_ref<'r, 'short: 'r, 'long: 'short>(long: &'r Self::Of<'long>) -> &'r Self::Of<'short> {
        unsafe { core::mem::transmute(long) }
    }
}
```

The proc macro (`ForLt!`) generates covariance proofs and well-formedness checks. The `visit_macro` handler conservatively assumes macro invocations may contain lifetimes:

```rust
fn visit_macro(&mut self, _: &syn::Macro) {
    self.1 = true;
}
```

The WF proof works around a Rust compiler soundness bug (rust-lang/rust#152489) by using a struct rather than a function to avoid implied WF bounds. The implementation is thorough -- the covariance prover handles references, pointers, tuples, arrays, slices, and falls back to compiler-checked proofs for complex types. Licensed Apache-2.0 OR MIT for future pin-init reuse.

One note: the `UnsafeForLtImpl` type is documented as "unsafe-to-refer-to" but there's no actual mechanism preventing misuse beyond doc comments. This is a known limitation of the pattern.

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Generated by Claude Code Patch Reviewer