chore(deps): move `fastify` to `devDependencies`

[dan-online]

With version 4.5.2 of fastify, the types were slightly different leading to a mismatch, therefore I moved fastify to a peer dependency for 4.x

[yonathan06]

Thanks for the PR! I know the peerDependencies can cause a lot of pain, why not moving fastify to devDependencies instead, I think we use it only for the types?

[dan-online]

Hey @yonathan06, How's this going?

[yonathan06]

@dan-online merged and released