EPIC CHECKLIST: Review/Integrate staged deposit-only ref impl work

[protolambda]

In the staging branch you can find a opnode dir with the reference implementation for the deposit-only milestone.
You can run it end-to-end with these instructions.

To simplify review, clean up the commit history, and help organize, we can split the staging branch into indepdent PRs:

• opnode/cmd + Go CI + go.sum file: boring boilerplate to run it as binary + CI setup, minimum compiling Go:
  ref impl: CI + opnode Go base #124
• opnode/eth: API interfaces, api utils and types:
  ref impl: eth utils - watch head, hash/height id type, RPC source interfaces #125
• opnode/l1: parallized/cached blocks and receipts downloader with tests:
  ref impl: L1 downloader of blocks and receipts #126
• opnode/l2/api.go: Execution Engine API client bindings:
  ref impl: Engine API client bindings #127
• opnode/l2/{reading.go, input_derivation.go}: convert block/receipts (interfaces for mocking in tests) to deposit transactions:
  ref impl: input derivation and reading l1-info #128
• opnode/l2/{output_derivation.go, driver_step.go}: where the we derive outputs and apply the block to the engine:
  ref impl: derive outputs and run driver step #129
• opnode/l2/{sync_reference.go, sync_start.go}: how we resolve where sync needs to start:
  ref impl: find starting point of sync, given L1 and L2 interfaces #130
• opnode/l2/driver.go: the main event system of engine sync:
  ref impl: driver agent: respond to head events and stay in sync #131
• opnode/node/: rollup-node start (init, manage and shut down all L1 and L2 processes):
  ref impl: main node process (connect with RPC, start drivers, handle shutdown) #132

[protolambda]

completed all PRs, closing this