This is just a temporary remedy to (hopefully) make the devnet CIs pass.
624 bytes = 8 (~L2 per L1 blocks) * 78 bytes (empty block with just Deposited tx)
It's a delicate dance.

Propoer fix is to observe channel timeouts and sequencer window span so
that we can set an even larger target but still send txs quickly enough
when there's now tx volume.

The block index handling had multiple bugs.

Better than replicating state.

It only checked whether the input target was reached. But it should
also close the underlying channel out if it is full for any other
reason.

Necessary after rebase.

Created an abstraction around channel creation, channelBuilder, that
tracks the amount of input rlp bytes and then decides when to close the
channel based on an estimated compression ratio.

- MinL1TxSize got renamed to TargetL1TxSize, it's the estimated target
  frame size
- TargetNumFrames is the estimated number of frames per channel
- ApprocComprRatio is the approximate compression ratio of the used
  compression algorithm (<= 1.0)

The improved tx batching algorithm needs to track the rlp encoded byte
size of added blocks and the frame number, so they are now returned by
ChannelOut to avoid state and computation duplication.

Bedrock frames have a fixed overhead of 23 bytes.

Also removed the extra byte that was reserved for the version because
the calling sites of OutputFrame() already subtract this byte from their
maxSize arguments. This makes sense because the calling sites are
responsible for handling the correct overall tx data size.

op-proposer: Move to shared signer setup & simplified init

This removes the NewL2OutputSubmitterWithSigner function and places
the old NewL2OutputSubmitter code inside the main function.

op-service: Migrate tx manager package

fix batch-deriv-chain.svg

This places the txmgr package in the op-service folder instead of
the op-proposer folder. This removes the proposer for being a dependency
of the batcher. The txmgr code is shared code so it makes more sense to
be there.

feat(e2e): Garbage batch test

feat: l1 and l2 source validation

fix spec/assets/engine.svg

whoops