refactor: eventstore with better error handling and stability

[hashemix]

📌 Summary

Enhanced EventStore trait with additional methods and event handling and stability

✨ Changes Made

• added count() method to the EventStore trait
• added prune_excess_events() method to the EventStore trait for removing events from the store using any custom logic like timestamp or capacity
• Introduced EventStoreError for better error handling support

🛠️ Testing Steps

cargo make check

💡 Additional Notes

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