refactor(proposer): Split REQ into PROVING & WITNESSGEN

[ratankaliani]

• Splits the REQ proof type into PROVING and WITNESSGEN. When a proof is in WITNESSGEN, it will be timed out after 20 minutes, with or without proposer restarts.
  • If you shut down the proposer and reboot it with the same DB, the WITNESSGEN proof will time out.
• Remove the off by 1 logic from the startBlock for simplicity. Now the ranges will overlap by 1 block. This makes sense, because the proofs need to be connected.
• Add documentation for ent generation.
• When determining the first unrequested proof, look for the unrequested proof with the earliest start block. This will prevent potential gaps in the proposer that will increase on-chain latency.
• Simplify some functions to use ProofRequest type directly.