Delimited File
@Serializable
A delimited text file on disk. Layout, delimiter, header policy, and column-role bindings together fully describe how to extract datasets.
SINGLE layout requires WHITESPACE delimiter and ignores hasHeader, idColumn, valueColumn, and datasetColumns.
WIDE layout requires COMMA delimiter and hasHeader = true. If datasetColumns is non-null, only those header names are imported, in the order given; otherwise every column is imported in file order.
LONG layout requires COMMA delimiter, hasHeader = true, and both idColumn and valueColumn set. Rows are grouped by id (first-seen order) into one dataset each.