feat: `SLOAD` optimized route and price

[xenide]

Currently

best case scenario:

• simple route
• num of SLOADs = 4
  • 1 for the existence of route
  • 1 for the length of the route array + first item
  • 1 for the second item of the array
  • 1 for the price cache

worst case scenario:

• 3 hop route
• num of SLOADs = 8
  • 1 for route query
  • 1 for length of route array + first item
  • 1 for second item of array
  • 1 for third item of array
  • 1 for fourth item of array
  • 3 for the price cache for 3 hops

Implemented solution

best case scenario:

• simple route
• num of SLOADs = 1
  • keccak256 token0-token1 and then loads 1 storage slot
  • reads price from that storage slot

Worst case scenario:

• 3 hop route
• num of SLOADs = 6
  • 3 for reading route
  • 3 for reading simple prices

Potential Further improvements

1. we can split some addresses over two words
   • i.e. storing 11 bytes in the previous word and then 9 bytes in the next word
   • e.g. 3 hop route (total 63 bytes of data)
     • instead of reading 3 slots for the route, we only have to read 2 slots
     • so we save 1 SLOAD
2. Storing the decimal multipliers in the unused bits in the slot
   • if we do this then we won't be able to do improvement no.1

Alternatives tried

1. Tried using the following:

mapping(address token0 => mapping(address token1 => bytes wtv))

Doesn't work because the the bytes will track length. So that's one more SLOAD

2. also tried

mapping(address token0 => mapping(address token1 => bytes wtv))[0:32]

doesn't even compile