Aggregates raw Ash records (returned by the read action) in memory into the stable labels/series output shape.

Output conventions (so a client-side chart adapter needs no per-type branching):

• :frequency (no group_by): labels = distinct column values; one series named after the column with the counts.
• :frequency (group_by): labels = distinct column values; one series per group_by combination, each series's data aligned to labels.
• :aggregate (no group_by): labels = [column]; one series named after the function.
• :aggregate (group_by): labels = distinct group_by combinations; one series named after the function.
• :time_bucket: labels = bucket labels; series per group_by combination (or a single series named after the function when there is no group_by).
• :percentile: labels = percentile labels; series per group_by combination (or a single series named after the column when there is no group_by).