feat: Add task related things to schema

[He-Pin]

Motivation and Context

ISSUE: modelcontextprotocol/modelcontextprotocol#1686
PR: modelcontextprotocol/modelcontextprotocol#1732

Issue in Java-sdk : #668

How Has This Been Tested?

Breaking Changes

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[He-Pin]

I will try to implement this internal first, feel free to continue

[He-Pin]

I would like to add modelcontextprotocol/modelcontextprotocol#1831 to this too

[Kehrlann]

Let's wait until the bizContext is resolved.

[He-Pin]

I'm ok to just drop it if time is not OK, and at the same time, I'm implementing it first internal too.

[Kehrlann]

Let's park this for now, then.

[He-Pin]

@Kehrlann Just dropped.

[He-Pin]

No | type in Java, so add the task here instead of GetTaskRequest | CallToolResult, an Either type will change much code, and Object loses type safety.

[He-Pin]

I was adding a CallToolAuxResult and I found the JSONRPCResponse has a JSONRPCError, so I will follow the same design. it should be JSONRPCResponse | JSONRPCError, but the current shape seems pratical.

[Randgalt]

Where are these in the spec? I don't find them.

[He-Pin]

My current implementation at work is Flux<McpMessage> callToolStream(CallToolRequest request) to support streaming responses. We also have callTool(CallToolRequest request) built upon this implementation.

I specifically plan to support streaming responses in the future. However, because my implementation at work is far more complex than a memory-based implementation, it's not yet ready for open-source development.

modelcontextprotocol/modelcontextprotocol#1905

[Kehrlann]

Closing in favor of #755 which adds the full task implementation.