2x pool depths for calculating swap fees for synthetic swaps

When swapping RUNE --> Synthetic or Synth --> RUNE, double the pool depths. This will cause the fees to be reduced for swapping synthetic assets over layer1 assets.

This incentivizes people to use synthetic assets over layer1. Not only because the swap fees are cheaper, but also the gas fees too (btc/eth gas fees are crazy high). This also makes trading more scalable, as some of the slower chains (BTC) doesn't have large enough blocks to handle all trades on layer1.