Symbol confusion after hasher panic in `intaglio` interners

Affected versions of this crate can leave all `SymbolTable` variants in an
internally inconsistent state if a custom `BuildHasher` panics during
`HashMap::insert` and the caller recovers with `catch_unwind`.

The `intern` implementations committed a `vec.push(...)` before the matching
`map.insert(...)` completed. If hashing panicked in that window, later lookups
and inserts could observe diverging `vec` and `map` lengths.

In release builds, this can lead to symbol confusion where a newly interned
string resolves to previously interned attacker-controlled contents. In debug
builds, the same corruption is detected by follow-up assertions and results in
panics.

The flaw was corrected in version 1.13.3 by making the `vec` mutation
transactional across unwind boundaries so partially inserted entries are rolled
back before the panic propagates.