Observation QA, event selection, and screen grouping

Use ps_check_observations() before mapping to inventory identifiers, coordinates, head, units, datum, event time, depth, and screen issues. Unusual values remain review flags. ps_select_event() then chooses at most one measurement per well under a recorded rule, while ps_screen_groups() preserves existing units or applies explicit rules. A time window is not proof of a synoptic event, and descriptive depth bins are not aquifers.

checked <- ps_check_observations(records, x="x", y="y", value="head", id="well")
event <- ps_select_event(records, "well", "time", center, window=86400)
groups <- ps_screen_groups(records, "rules", screen_top="top",
                           screen_bottom="bottom", rules=unit_rules)