fix: propagate errors from async trusted callback

[Nadav0077]

What this PR does

When a user supplied trusted callback returns a rejected promise, the rejection was silently dropped. .then(...) had no onRejected handler, so:

• steed.waterfall's final callback was never invoked and the request hung.
• The rejection surfaced as an unhandledRejection on the Node process.

Fix

Pass the onRejected handler to .then(...) so the error flows to the waterfall's terminal callback, matching the behavior of every other step.

Test

Added Trusted token, async verification rejects in test/jwt.test.js. It registers a trusted callback that returns Promise.reject(new Error('boom')) and asserts the error reaches the route handler (status 500, message === 'boom'). The test fails on main and passes with the fix.

Checklist

• run npm run test && npm run benchmark --if-present
• tests and/or benchmarks are included
• documentation is changed or added (no API or doc change, purely a bug fix)
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[mcollina]

lgtm