Support Fastify 5 in @connectrpc/connect-fastify

[boan-anbo]

Is your feature request related to a problem? Please describe.
Support the Fastify v5: https://github.com/fastify/fastify/releases/tag/v5.0.0

Describe the solution you'd like
Can support the Fastify v5 and install the npm plugin package without conflicts. Currently it shows a conflict between 4.22.1 which [email protected] uses.

[srikrsna-buf]

Thank you for opening the issue, we definitely want to support v5. Can you send a PR for this?

[timostamm]

From a quick look at the migration guide, this should be simple.

We can relax the peer dependency constraint to accept v5, and update conformance-fastify.yaml to only run in Node.js v20 and later.