Raise NotImplementedError for Monarch-style Methods on ServiceEndpoint

[DNXie]

A follow up on #222
This pull request introduces explicit error handling for Monarch-style methods (call_one, broadcast, generate, choose, call) on the ServiceEndpoint class. Attempting to invoke these methods on a service endpoint will now raise a NotImplementedError with a clear message indicating that these operations are only supported for actors, not services. The error message guides users to use the supported route() and fanout() methods for service endpoints.

Testing

• Added test_service_endpoint_monarch_method_error to ensure that each unsupported method raises the correct exception and message.
• All existing and new tests pass.