feat: Light block builder

[spalladino]

Adds a block builder that assembles an L2Block out of a set of processed txs without relying on base, merge, block root, or parity circuits, and works using only ts code. Keeps the same interface as the current block builder for drop-in replacement within the orchestrator.

Replaces the orchestator-based block builder on the sequencer. In a 32-tx block with a simple public function per tx, this reduces block building time from 38 to 18 seconds.

aztec:sequencer [VERBOSE] Assembled block 5 (txEffectsHash: 00a201e4acd5f1d58d8369d385f3fa0a7c10c84c1a95c15c75844603660f5ff3) eventName=l2-block-built duration=18983.888042002916 publicProcessDuration=18955.1897890009 rollupCircuitsDuration=18983.70012800023 txCount=32 blockNumber=5 blockTimestamp=1726864978 noteEncryptedLogLength=256 noteEncryptedLogCount=0 encryptedLogLength=256 encryptedLogCount=0 unencryptedLogCount=0 unencryptedLogSize=384 +19s

aztec:sequencer [VERBOSE] Assembled block 5 (txEffectsHash: 00414283d876d3b97871a671bc18660222211c7baa9eb106da5215b998752320) eventName=l2-block-built duration=38610.87693199888 publicProcessDuration=19141.498885001987 rollupCircuitsDuration=38610.68504599854 txCount=32 blockNumber=5 blockTimestamp=1726865139 noteEncryptedLogLength=256 noteEncryptedLogCount=0 encryptedLogLength=256 encryptedLogCount=0 unencryptedLogCount=0 unencryptedLogSize=384 +39s

[MirandaWood]

Looks great! 🚀