addToGroup abstract method
Adds an event to a named group for batch operations.
Groups allow emitting multiple related events at once via emitGroup. If the group doesn't exist, it's created automatically.
groupName: The name of the group (e.g., 'user.events').event: The event name to add to the group.
Example:
events.addToGroup('auth', 'user.login');
events.addToGroup('auth', 'user.logout');
Implementation
void addToGroup(String groupName, String event);