Renders a counts report — per-feature cell occupancy.
Parameters
counts: Counts
Returns string
Remarks
getCounts answers "how much of each feature is here"; stats answers "what are the values
like". Zero features are elided — the record's stable full-key shape is an API property, not
a reporting one; a report of twenty zeros buries the four numbers that matter.
Renders a counts report — per-feature cell occupancy.