strat vs strata (vs strata_var)

[pawelru]

There are few places where we use strat and strata (and also strata_var) which seems to be inconsistent.

It might be working if strat is required and strata is provided due to R's ability of partial match but we should avoid it (there is a seperate PR aims to punish it). The other way around is not functional.

Please analyse if that's correct.

If to be corrected, note that it's potentially a breaking change so would be nice to give a lifecycle warning and create strata from strat (or vice versa).

This has downstream consequences in chevron, tmc and TLG-Cat - if changed please amend these as well.