ErrMsgNotFound is the error message for when a resource is not found.

ErrMsgSaveFailed is the error message for when a save operation fails.

ErrNotFound is an error for when a resource is not found.

ErrSaveFailed is an error for when a save operation fails.

Number is a struct to represent a number.

GrpcServer is an interface for gRPC server.

IConfig is an interface for configuration.

INumberRepository is an interface for number repositories.