swaps: build index(es) for the swaps dict to avoid linear scanning
swaps: build index(es) for the swaps dict to avoid linear scanning

spesmilo/electrum,pooler/electrum-ltc,spesmilo/electrum,spesmilo/electrum,pooler/electrum-ltc,spesmilo/electrum,pooler/electrum-ltc,pooler/electrum-ltc