Task: Add Resource Links in Tool Results

[ezynda3]

Priority: Medium
Breaking Change: No

Description: Tool calls can now return ResourceLinks in addition to full EmbeddedResources in results.

Implementation Tasks:

• Add ResourceLink type with discriminator
• Update ContentBlock union to include ResourceLink
• Add support in tool result handling
• Update examples to show resource linking
• Add tests for resource link functionality

Files to Update:

• mcp/types.go
• mcp/tools.go
• Content handling code