Move table helpers to this repo

Move `tabular?` and `view-as-table-viewer` helpers [from ductile](https://github.com/nextjournal/ductile/blob/089f5d442332d6819080832fe657979f2cfcf521/src/ductile/reporting/inventory.clj#L11-L22) to this repo. Afaiu the overall goal is to drop the table viewer in ductile in favour of using this repo.