Implement SEP-1319: Decouple Request Payload from RPC Methods

[DaleSeo]

Fixes #523

Implments SEP-1319 to comply with the 2025-11-25 MCP spec.

Motivation and Context

To decouple request payloads from RPC method. For more details, see modelcontextprotocol/modelcontextprotocol#1319.

• Renames all *RequestParam to *RequestParams (plural) to match the updated schema reference
• Moves _meta (containing progressToken) from the JSON-RPC envelope into the params struct itself
• Introduces RequestParamsMeta and TaskAugmentedRequestParamsMeta traits to model the spec's interface inheritance

Used modelcontextprotocol/typescript-sdk#1086 as a reference implementation.

How Has This Been Tested?

• All existing unit and integration tests pass
• JSON schema tests updated to reflect new struct names
• Verified _meta field serializes correctly with #[serde(rename = "_meta")]

Breaking Changes

The existing code will compile with warnings with the migration path:

• Deprecated type aliases provided for all renamed types
• Handler trait method signatures updated to use new types
• New meta: Option<Meta> field added to all param structs (defaults to None)

There is a compile-time breaking change, even when using the deprecated alias. When constructing structs directly (not via deserialization), users must now add meta: None:

// Before
CallToolRequestParam {
    name: "tool".into(),
    arguments: None,
    task: None,
}

// After
CallToolRequestParam {
    meta: None,         // NEW REQUIRED FIELD
    name: "tool".into(),
    arguments: None,
    task: None,
}

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