Seconds-per-kilometre → "m:ss/km" (default) or "m:ss/mi" when unit is
imperial. Rounds total seconds first then splits, so a pace rounding up to
a full minute carries (119.88 → "2:00/km", never "1:60/km"). Same
round-then-split discipline as formatDuration.
Seconds-per-kilometre → "m:ss/km" (default) or "m:ss/mi" when
unitis imperial. Rounds total seconds first then splits, so a pace rounding up to a full minute carries (119.88 → "2:00/km", never "1:60/km"). Same round-then-split discipline as formatDuration.