This change adds Jackson 3 support and aligns package naming in the existing Jackson 2 module.
Specific changes:
* Deprecated classes for removal in `io.modelcontextprotocol.json.jackson`/`io.modelcontextprotocol.json.schema.jackson`
* Copied the above to `io.modelcontextprotocol.json.jackson2`/`io.modelcontextprotocol.json.schema.jackson2` in non-deprecated form.
* Added tests for the default McpJsonMapper and JsonSchemaValidator