Remove the unique constraint on the 'cif' field in the debitures table and refactor the `UniqueCifExceptZero` validation rule to handle the uniqueness check more robustly. Also, add an unused import statement for `UniqueExcept` in `DebitureRequest`.
Remove the unique constraint on the 'cif' field in the debitures table and refactor the `UniqueCifExceptZero` validation rule to handle the uniqueness check more robustly. Also, add an unused import statement for `UniqueExcept` in `DebitureRequest`.