fix: handle malformed URNs without throwing

[mcollina]

Normalize and equal now treat an ordinary URN that fails scheme-specific parsing (a missing nid) as malformed input instead of surfacing an uncaught URN without nid cannot be serialized error.

• normalize preserves the original malformed string unchanged
• equal returns false instead of throwing
• resolve rejects the malformed scheme-specific input with a clear URI is malformed. error

This is the follow-up to the URN parsing anchoring in #203, which now rejects more malformed inputs and so exposed the throw path. A new malformedSchemeSpecific status flag is threaded through the status-carrying helpers (parseWithStatus, normalizeStringWithStatus, normalizeComparableURI, resolve).

[Tony133]

LGTM! A small, non-blocking suggestion: it might be worth adding a test that calls resolve() with an invalid URN to check the actual error message, since that path is currently only covered indirectly. What do you think?

[mcollina]

Implemented Tony's suggestion: added a resolve handles malformed ordinary URNs without throwing test in test/malformed-urn.test.js that directly calls resolve() with each malformed URN (as both a relative reference and a base URI), asserting it does not throw and preserves the malformed scheme-specific input.

Note: resolve() does not actually raise a URI is malformed. error for malformed URNs — it preserves the input, which matches upstream uri-js. The new test locks in that actual behavior so the path is covered directly rather than only indirectly.

[Tony133]

There are conflicts in the malformed-urn.test.js file