fix: route cleanup

[alanshaw]

The binding package is the outer layer sugar, it can depend on lower levels but lower levels should not depend on it.

This PR moves the NewRoute[Args, OK CBORValue](cmd Binding[Args, OK], fn HandlerFunc[Args, OK]) function to the binding package and adds a Route(...) method to Binding allowing users to create a route directly from the binding (similar to Handler(...)).

The Route type stays in server package since it is a useful container type even if you're not using the binding package.

I've added a NewRoute(cmd ucan.Command, fn execution.HandlerFunc) to server in place of the binding specific NewRoute for convenience.