Resolves the presenter <cngx-timeline> builds its bands with.
Defaults to createTimelineGrouping.
Override app-wide via
providers: [{ provide: CNGX_TIMELINE_GROUPING_FACTORY, useValue: myFactory }]
to change bucketing everywhere (fiscal calendars, "today / earlier"
relative bands, server-supplied grouping), or per component via
viewProviders for a one-off. An override wraps rather than replaces
in most cases - call createTimelineGrouping inside your factory and
post-process its groups.
Same shape as CNGX_SELECTION_CONTROLLER_FACTORY: the internals of a
component are swappable without forking the component.