Mcp-core has compile-time dependency on mcp-json

[scottslewis]

mcp-core project has a compile-time dependency on mcp-json due to the location of these three classes:

/mcp-json/src/main/java/io/modelcontextprotocol/json/McpJsonMapper.java

/mcp-json/src/main/java/io/modelcontextprotocol/json/TypeRef.java

/mcp-json/src/main/java/io/modelcontextprotocol/json/schema/JsonSchemaValidator.java

I would argue that since these classes are required at all times, it doesn't make sense for them to be in a separate jar...as mcp-core jar is useless without mcp-json jar also present.

I would suggest moving these three classes (at least) back to mcp-core (e.g. in package io.modelcontextprotocol.sdk.util or io.modelcontextprotocol.sdk.json. This would allow a clear separation between mapper and schema validator interfaces (in core) and their implementation (default or other).