resolves #3402

This PR implements the "Double Schema Bucket" feature discussed in #3402 to resolve compatibility issues when passing schemas containing newer JSON Schema drafts (e.g., 2020-12) to both ajv (which supports it) and fast-json-stringify (which throws errors as it only supports up to draft 07).

Changes:

• lib/schema-controller.js: Split the core schema container into discrete validatorBucket and serializerBucket instances.
• fastify.js: Added an options parameter to addSchema(schema, options) supporting { validator?: boolean, serializer?: boolean } config object.
• types/instance.d.ts: Updated TypeScript definitions for the new options argument and exposed getters.
• test/schema-double-bucket.test.js: Added unit tests to ensure scopes do not leak when adding schemas targeted at specific compilers.

Note: The feature is completely backward compatible. Calling addSchema(schema) without options continues to add the schema to both buckets as it always has.

Checklist

• run npm run test && npm run benchmark --if-present
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct