Is your feature request related to a problem? Please describe.
I really appreciate the FastMarkerCluster that allows me to plot over 300K markers and keep both a reactive map and a not so big generated HTML size (10 times smaller than MarkerCluster, so in my case 30MB vs 300MB).
However, as far as I understand, we loose the ability to manage groups ... with MarkerCluster it was possible to define several FeatureGroupSubGroup objects so that I could show/hide a subset of my data (e.g. markers for 2G / 3G / 4G / 5G mobile cells coordinates).
Could this be done with FastMarkerCluster ???

Describe the solution you'd like
Have FastMarkerCluster handle groups that are controlled through the Layer Control.

Describe alternatives you've considered
None

Additional context
In the below map snapshot, I am using FastMarkerCluster to plot 2G (black) / 3G (gray) / 4G (blue) / 5G (red) cells. The cell color is handled in the callback though a network_type attribute that is provided in addition to latitude and longitude.
Instead of a single item "Cell coordinates", I'd like to have 4 items based on the cell technology.

Implementation
Not sure to have the requested knowledge yet ...