Add pretty library

[aviggiano]

This: https://github.com/one-hundred-proof/kyberswap-exploit/blob/main/lib/helpers/Pretty.sol
by @one-hundred-proof

[x100proof]

I'm so glad this got some use. Only in retrospect do I realise how useful this random idea was. The best thing about it is that you can copy/paste the numbers straight into Foundry's chisel without having to e.g. remove commas/delete periods.