Bug description
The JsonSchema class is not accessible outside of its package. It would seem that
https://github.com/modelcontextprotocol/java-sdk/blob/main/mcp/src/main/java/io/modelcontextprotocol/spec/McpSchema.java#L670 needs to be made public.

Environment
Using the Mcp Client:
implementation(platform("io.modelcontextprotocol.sdk:mcp-bom:0.7.0"))
implementation("io.modelcontextprotocol.sdk:mcp")

Expected behavior
The JsonSchema should be accessible.

Minimal Complete Reproducible example
I am currently working on integrating MCP in our kotlin AI Agent Framework
https://github.com/eclipse-lmos/arc/blob/main/arc-mcp/src/main/kotlin/McpTools.kt.
Currently when trying to access the field tool.inputSchema it cannot compile.
I can set this up so that the error can be reproduced, if that helps.

Thanks a lot! And great work!