A reconnecting volume server reports every volume it has as new, so newVolumes
grew from nil to one entry per volume, reallocating and copying its way there.
Sizing it to len(actualVolumes) instead would allocate the whole list on every
steady-state heartbeat, where nothing is new.
After the deletion pass everything left on the node is also in this heartbeat,
so the difference is exactly what the node is about to gain: all of them on a
reconnect, none in steady state.
First registration of 550k volumes 1041.7 MB -> 667.4 MB