Implement a routing library

[whoabuddy]

Right now we are manually routing the endpoints to functions with string matching. This works but could get messy as things grow.

We should look into a routing library that maintains the same clean, simple structure we're using now. I think itty-router would be a good fit but def needs some testing and high-level thought. Open to feedback.

[whoabuddy]

For now I've split the database file into handlers, where the durable object passes the request to the handler and it iterates over its endpoint operations in a switch statement. It's still a simple implementation but helps break things up to make them easier to read.