CofacetCursor

A hasNext/vertex/index/advance() cursor over sigma's cofacets, factored out of what cofacetIteratorWithVertex used to do directly as a hand-rolled Iterator[(Int, Long)], so a caller can read vertex/index as plain field accesses with zero per-step allocation -- not even the (Int, Long) tuple an Iterator[(Int, Long)] contract forces on every next() call. hasNext/advance() are deliberately split from a single next(): vertex/index stay valid to re-read as many times as a caller wants between one advance() and the next (both PackedRipserCohomology.scala's coboundaryOf and Homology.scala read both fields off one candidate before advancing).

Decodes sigma via decodeToArray (a plain sorted Array[Int], binary-searched for membership), not apply (a Simplex[Int]/SortedSet[Int], O(log d) tree lookup per membership check) -- the same array-over-tree substitution decodeToArray's own doc motivates, folded in here since this cursor replaces cofacetIteratorWithVertex's body outright rather than wrapping it.