Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the feature has not already been requested

🚀 Feature Proposal

I propose to make the param of the send method 'required' in the type declaration.
This way, if you do not use any RouteGenericInterface or TypeProvider, you will be free to pass anything to send, including nothing.
But, if you use any RouteGenericInterface or TypeProvider, the type checker will be more strict. You will not be able to reply undefined for a required reply's payload specified through TypesProvider or RouteGenericInterface.

Motivation

My motivation was this issue turkerdev/fastify-type-provider-zod#88

In this issue, the user asks about a more restricted type checking for replies.

Example

const server = fastify()

interface ReplyHttpCodes {
  Reply: {
    201: string
    204: undefined
  }
}

server.get<ReplyHttpCodes>('/', async function handler (request, reply) {
  reply.status(201).send('some string') // No Error
  reply.status(204).send() // No Error
  reply.status(204).send(undefined) //No Error

  reply.status(201).send() // TS Error: Expected 1 arguments, but got 0 (My PR introduced this checking)
  reply.status(201).send(123) // TS Error: Argument of type 'number' is not assignable to parameter of type 'string'
  reply.status(204).send('543534') //TS Error: Argument of type 'string' is not assignable to parameter of type 'void' 
})