Initial project structure for MCP variants

[Degiorgio]

Establishes a multi-language monorepo structure for MCP Variants. Implements an efficient CI/CD system that only tests what changes.

🏗️ SDK Scaffolding

• Python SDK (python/sdk/)
• TypeScript SDK (typescript/sdk/)
• Go SDK (go/sdk/)
• Monorepo structure: Consistent {language}/sdk/ pattern across all implementations

🚀 CI/CD Pipeline

• Path-based workflow triggering: Only runs CI for languages that actually changed
  • Change Python → only Python CI runs
  • Change multiple languages → only those CIs run
• Status check workflow: Single required check that dynamically validates based on changes
• Comment triggers: Maintainers can run all checks with /test all PR comment