Normalise and validate a list of state codes: trims, upper-cases, de-duplicates
(preserving order) and rejects anything not among the 16 known codes (see
statesProblem) with a HochwasserzentralenValidationError ("Invalid
states: ") — so a typo never becomes a silently-dropped filter that
returns the full nationwide set. Idempotent; the CLI's --states uses it too.
Normalise and validate a list of state codes: trims, upper-cases, de-duplicates (preserving order) and rejects anything not among the 16 known codes (see statesProblem) with a HochwasserzentralenValidationError ("Invalid states:") — so a typo never becomes a silently-dropped filter that
returns the full nationwide set. Idempotent; the CLI's --states uses it too.