test(precedence): strengthen accounting test, cover order and empty sanctoral

The accounting test only checked bucket lengths, which a mutant satisfies by
duplicating a candidate across two buckets while dropping another entirely.
Replace it with a sorted slug-set comparison (Alcotest.slist), which a
duplicate-or-missing slug both fail.

Add two cases the brief's three properties call for but nothing exercised:
input-order independence (permuting the sanctoral list must not change the
outcome) and a temporal-only day (empty sanctoral list), the case the
temporal/sanctoral split exists to make safe.

0 files changed, 0 insertions, 0 deletions