Add challenge API to sha256

[Brechtpd]

• Code can be found here: sha256 circuit privacy-scaling-explorations/zkevm-circuits#756
  • Some info on how it works: https://docs.google.com/presentation/d/1eHVzLPRIEziCJ_oDuJG0yZ-5klNj_daqioC0UaGDaiw/edit#slide=id.p
• First merge it against the current PSE master
• Then integrate the challenge API: https://www.notion.so/taikoxyz/halo2-Challenges-API-review-d81d5c0bc1bc496fa303aa1561bb36f5
• Integrate as a precompile in the EVM circuit. Sample: Identity (dataCopy) precompile privacy-scaling-explorations/zkevm-circuits#1396
• Then do the Lo/Hi split for the hash value (similar to keccak/other circuit)
• Then make the layout more flexible if possible (especially allowing the circuit to be more narrow (use fewer columns))