close abstract method
Shuts down the dio client.
If force is false (the default) the Dio will be kept alive
until all active connections are done. If force is true any active
connections will be closed to immediately release all resources. These
closed connections will receive an error event to indicate that the client
was shut down. In both cases trying to establish a new connection after
calling close will throw an exception.
Implementation
void close({bool force = false});