Revisit schema. Generate Kotlin code from json-schema

[devcrocod]

Currently, the model classes are written by hand and not in sync with the specification.

The good news is that there is a Json-Schema for the protocol and pojos can be generated automatically.

ToDo

• Consider openapi-generator gradle plugin to generate model classes. Generate classes to io.modelcontextprotocol.kotlin.sdk.model
• Remove generated classes out of types.kt. types.kt has degraded; it has become too huge. Consider extending hand-written classes from generated ones, marking hand-written classes as deprecated and remove them completely on the next releae
• Move serializers to a separate package, e.g. io.modelcontextprotocol.kotlin.sdk.model.serializers.
• Add comprehensive JSON serialization/deserialization tests

DoD

• Model classes are generated as a build step from the JSON schema
• Unit tests for JSON serialization exist and are green. Test coverage is 100% for model classes. Take sample jsons from the latest specification