fix: Panic when an extension name is too long. (#2198)

This PR fixes a bug that led to a panic in import when the name of an
extension exceeded 23 bytes.

This was caused by a misreading of `IdentList::new_unchecked`: this
method not only avoids checking the identifier for validity but also
assumes that the input will fit into the 23 byte inline capacity of a
`SmolStr`.

Author: zrho

hugr-core/src/hugr/ident.rs

@@ -59,7 +59,7 @@ impl IdentList {
     #[must_use]
     pub fn split_last(&self) -> Option<(IdentList, SmolStr)> {
         let (prefix, suffix) = self.0.rsplit_once('.')?;
-        let prefix = Self::new_unchecked(prefix);
+        let prefix = Self(SmolStr::new(prefix));
         let suffix = suffix.into();
         Some((prefix, suffix))
     }