fix: set finalized & safe block information on startup

[danyalprout]

Description

Currently when you restart Reth, fetching blocks by finalized or safe block returns "block not found". This causes an issue when running op-reth via consensus layer sync, as it'll cause op-node to walk the chain back to genesis.

This PR loads the finalized block number from the database and initializes it on startup. It'll also set the safe block equal to the finalized value -- as the finalized block is also safe.

You can repro this bug on main with the following steps:

# set safe/finalized head via forkchoice update

# Fetch the finalized block
curl localhost:8545 \
  -X POST \
  -H "Content-Type: application/json" \
  --data '{"method":"eth_getBlockByNumber","params":["finalized",false],"id":1,"jsonrpc":"2.0"}' | jq
{... block info}

# restart reth

# Fetch the finalized block
curl localhost:8545 \
  -X POST \
  -H "Content-Type: application/json" \
  --data '{"method":"eth_getBlockByNumber","params":["finalized",false],"id":1,"jsonrpc":"2.0"}' | jq

{
  "jsonrpc": "2.0",
  "error": {
    "code": -39001,
    "message": "unknown block"
  },
  "id": 1
}

[joshieDo]

We only recently started storing the last finalized block, so this makes sense overall, even beyond op-reth.

But given how op-node switches between el-sync and cl-sync on boot-up, this will have the effect that a node won't use our staged sync beyond the first time syncing. (eg. stopping the node for a week, and starting it again).

[mattsse]

@joshieDo confirming we still want this?

[danyalprout]

@joshieDo FYI I'm going to test this now with engine kind reth param from ethereum-optimism/optimism#10767 and see if it works as expected.

[danyalprout]

@joshieDo was able to restore from a snapshot and it would EL sync from the snapshot to tip -- without having to walk back to genesis.