Infinitely recursive `dyn`

As discovered by @theemathas at https://github.com/rust-lang/rust/issues/142900#issuecomment-2994854291, the following compiles:

```rust
trait Trait: Sync {}

impl Trait for &dyn Trait {}

static X: &dyn Trait = &X;
```

Perhaps this is too obscure even for the quiz, but I’m sure it’s possible to make a fun question based on this trick.

Start by compiling the Rust example from the issue and reviewing the repository's existing quiz questions and explanations for their format and difficulty. Develop a question around the infinitely recursive dyn behavior, with an explanation that makes the trick understandable; done means a suitable quiz entry is proposed or added.

Written by the indexing model from the issue text.