`pareto_front` re-scanned every candidate from scratch. Track a
`dominated` bitset instead: whenever `i`'s scan finds `i` dominates `j`,
mark `j` so the outer loop skips `j` outright when it reaches it. The
inner check now reads both directions of `pareto_compare` — the
objective scan already computes both flags, so this is ~free.
Bit-identical, including under NaN-intransitive dominance: a mark is
only ever set from a direct pairwise `pareto_compare` result, never
inferred transitively. Also strict-or-neutral on work — the marks can
only ever let the outer loop *skip*, never add a scan.
Whole-program callgrind Ir for the compare_profile benchmark:
169,440,644,233 -> 165,311,562,939 (-2.44%); `pareto_front` self-Ir
44.1B -> 39.9B.
swaits
a4b11f286e