fix(sequencer): respect max_tx_bytes when preparing proposals (#911)

## Summary
Ensures that `cometBFT` blocks will not become too large during
`prepare_proposal()` from the addition of commitments to the front of
the block.

## Background
`cometBFT` sends in a `max_tx_bytes` parameter to the ABCI
`prepare_proposal()` that should be respected when modifying the block.
We currently add commitments to the front of the block for the included
rollup ids and included rollup transactions. It is possible that adding
these bytes will cause the `cometBFT` block to be larger than the
`max_tx_bytes` parameter.

## Changes
- Refactored `execute_block()` into `execute_block()` and
`execute_and_filter_block()` and pulled out the shared logic into
`execute_transaction()`.
- Prevents `cometBFT` blocks from becoming too large from adding the
commitments to the front of the block.

## Testing
- Added new unit test ensuring that overflow is okay.
- Ran local setup to ensure that transactions still flow through the
system in general.

## Issues
closes #850