Handle arbitrages with split swaps

[lukevs]

Currently we expect arbitrages to look like

Token 1 --> Pool A (100%) --> Token 2 --> Pool B (100%) --> Token 1

But it's possible to do something like

Token 1 --> Pool A (100%) --> Token 2 --> Pool B (50%) --> Token 1 --> Pool C (50%)

which we don't currently support