Avoid JSON.stringify calls

Yes, it is so right now.

I would open an issue for it and leave it as-is right now

The solutions I see:

- track the [ajv options](https://github.com/ajv-validator/ajv/blob/master/docs/api.md#options) to write a fast-json-stringify function that serialize them instead of `JSON.stringify`
- apply a new logic like:
- check the number of keys
- check iteratively the values (I see only primitive types as values)

_Originally posted by @Eomm in https://github.com/fastify/ajv-compiler/pull/1#discussion_r588874508_