Add support for the optional `websiteUrl` parameter in `serverInfo`

[koic]

Motivation and Context

This PR adds support for the optional websiteUrl parameter in serverInfo. This parameter has been supported since the 2025-11-25 MCP specification.

This PR also implements part of https://github.com/modelcontextprotocol/ruby-sdk/issues/127.

How Has This Been Tested?

The tests have been updated and are now passing.

Breaking Changes

None.

Types of changes

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

Checklist

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