refactor: expose Store Traits and add ToMcpServerHandler for Improved Framework Flexibility

[hashemix]

📌 Summary

This PR introduces the following improvements to enhance extensibility and framework flexibility:

✨ Changes Made

• Exposed SessionStore and EventStore traits:
  These traits are now publicly available so users can implement their own custom stores if needed.
• Exposed default store implementations: InMemorySessionStore and InMemoryEventStore .
• Introduced ToMcpServerHandler trait: a new trait with a default implementation for converting types into Arc<dyn McpServerHandler + 'static>.
  This abstraction will be instrumental in making the SDK HTTP-framework agnostic, supporting a broader range of frameworks in the future.

🛠️ Testing Steps

cargo make check

💡 Additional Notes

This is another step toward making the SDK more framework-agnostic, with future support planned for HTTP frameworks like Actix and serverless environments such as AWS Lambda.