DowkerFiltration

DowkerGeometry.filtrationValue, memoized -- the same "a caller-supplied filtrationValueOverride is not cached by RipserCofaceSimplexStream itself, so a genuinely expensive one must cache itself" reasoning as CechFiltration/WitnessCofaceSimplexStream.recursiveFiltrationValue. Deliberately no spx.dim 0.0 special case (contrast CechFiltration/MaximumDistanceFiltrationValue): a Dowker vertex's own filtration value is generally nonzero and meaningful, not a VR-style convention-only placeholder -- see the class doc.