When there are unprefixed savetos across sibling groups, entity declaration is too low to capture all savetos

[lognaturel]

Forum post: https://forum.getodk.org/t/when-using-groups-entity-fields-only-processing-in-first-group-ignored-elsewhere/57809

This means forms that used to work in prior versions of pyxform are broken in 4.3.0 so it feels like a priority to address.

[lognaturel]

This likely has the same root cause as #822, #823, #825. I didn't explore whether using prefixes makes any difference. Could we consider doing a check that all savetos are "covered" by a declaration?