`Circuit::wrap_package` does not add extensions to Package

[doug-q]

My hugr, which included non-std extensions, was invalid after passing through tket.

The following fixed it:

    fn wrap_package(&self) -> Result<Package, EnvelopeError> {
        let hugr = Circuit::to_owned(self).into_hugr();
        let extensions = hugr.extensions().clone();
        let mut package = Package::from_hugr(hugr);
        package.extensions.extend(extensions);
        Ok(package)
    }

The docs for Package::from_hugr say you must manually add extensions.
There is another from_hugr callsite in opaque/payload.rs that may have a similar issue.