feat: Support Nested Content Types (cs97dah - renewed)

[breandanh-kf]

Hey!

Firstly, thank you taking the time to make and maintain this library!

I've just (within the last month or so) started using it and after a quick search noticed it was missing this feature, and wanted to contribue back to the community with it.

I hope I've created this the way you're expecting for suggested changes. Of course, looking for feedback, I expect that I have probably missed something.

The changes made are an extension of the changes made by @cs97dah:
#89

I've just re-moulded them to match the new structure of the code (which seems to have changed since this PR was first created). I've also included some other use-case examples in the tests based on the features documented by fastify themselves: https://fastify.dev/docs/latest/Reference/Validation-and-Serialization/#serialization.

This change allows for the following schema definition example:

fastify.post('/url', {
  schema: {
    response: {
      200: {
        description: 'Response schema that support different content types'
        content: {
          'application/json': {
            schema: z.object({
              name: z.string(),
              image: z.string(),
              address: z.string(),
            })
          },
          'application/vnd.v1+json': {
            schema: z.arrayOf(TestSchema)
          }
        }
      },
      '3xx': {
        content: {
          'application/vnd.v2+json': {
            schema: z.object({
              fullName: z.string(),
              phone: z.string()
            })
          }
        }
      },
      default: {
        content: {
          // */* is match-all content-type
          '*/*': {
            schema: z.object({
              desc: z.string()
            })
          }
        }
      }
    }
  }
});

It should (if accepted) resolve the following issues:

• feat: add support multi content in schemas #178
• Should handle different content types in body and response #132

[Mikescops]

@kibertoad @turkerdev any updates on this PR?

[acidoxee]

I'm very interested as well in this PR's resolution! I'm trying to migrate from @fastify/type-provider-typebox to fastify-type-provider-zod, and right now we can't do a 1-1 migration since detailed schemas with content don't seem supported.

Is there a blocker to this PR?