const impl formatting doesn't work

It seems the const impl syntax isn't being pasrsed!

```
thread '' (78880) panicked at ...\index.crates.io-1949cf8c6b5b557f\prettyplease-0.2.37\src\item.rs:364:13:
not implemented: Item::Verbatim `impl const std :: ops :: Deref for cLockableTexture < > { type Target = crate :: bindings :: Hw :: Graphics :: cTexture < > ; fn deref (& self) -> & Self :: Target { & self . base } }`
```

Start by reproducing the panic with the const impl syntax shown in the issue, then inspect the formatting path around the reported dependency location, src/item.rs:364:13. Confirm that const impl input is parsed and formatted without producing Item::Verbatim or panicking; add a regression test if the repository’s test structure identifies an appropriate location.

Written by the indexing model from the issue text.