add support for resource metadata

[mat-octave]

Adds support for including metadata in the mcp.resource decorator.

Motivation and Context

This is required by OpenAI to support the Content Security Policy.

How Has This Been Tested?

I added metadata to a resource from my MCP server, then called resources/list with the MCP Inspector. The metadata was in the resource schema.

Breaking Changes

Nope, it's all optional keywords

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