fix: support array hooks in setNotFoundHandler

[0XFF-96]

Summary

LInk: #174

• Support array values for setNotFoundHandler preValidation and preHandler hooks.
• Wrap each hook individually so Fastify receives callable handlers.
• Preserve callback names for each generated hook span.
• Add regression coverage for custom 404 handlers using hook arrays.

Root cause

The not-found handler patch passed the entire hook array to handlerWrapper(). The wrapper later called handler.call(...), causing handler.call is not a function and a 500 response.

Verification

• npm test
• npm run lint