fix: Pad L1 to L2 messages upon retrieval from L1

[PhilWindle]

This PR fixes a bug where L1 to L2 message padding is lost upon retrieval from L1.

Checklist:

Remove the checklist to signal you've completed it. Enable auto-merge if the PR is ready to merge.

• If the pull request requires a cryptography review (e.g. cryptographic algorithm implementations) I have added the 'crypto' tag.
• I have reviewed my diff in github, line by line and removed unexpected formatting changes, testing logs, or commented-out code.
• Every change is related to the PR description.
• I have linked this pull request to relevant issues (if any exist).

[AztecBot]

Benchmark results

All benchmarks are run on txs on the Benchmarking contract on the repository. Each tx consists of a batch call to create_note and increment_balance, which guarantees that each tx has a private call, a nested private call, a public call, and a nested public call, as well as an emitted private note, an unencrypted log, and public storage read and write.

This benchmark source data is available in JSON format on S3 here.

Values are compared against data from master at commit cb18f455 and shown if the difference exceeds 1%.

L2 block published to L1

Each column represents the number of txs on an L2 block published to L1.

Metric	8 txs	32 txs	128 txs
l1_rollup_calldata_size_in_bytes	45,444	179,588	716,132
l1_rollup_calldata_gas	223,020	868,220	3,449,552
l1_rollup_execution_gas	842,107	3,595,328	22,204,921
l2_block_processing_time_in_ms	1,019 (-2%)	3,897 (-3%)	15,334 (-2%)
note_successful_decrypting_time_in_ms	323 (-2%)	991 (-2%)	3,672 (-2%)
note_trial_decrypting_time_in_ms	⚠️ 25.0 (-26%)	100 (-7%)	137 (-1%)
l2_block_building_time_in_ms	8,948 (-1%)	35,770 (-1%)	150,348 (-1%)
l2_block_rollup_simulation_time_in_ms	6,617 (-2%)	26,486 (-1%)	105,397 (-2%)
l2_block_public_tx_process_time_in_ms	2,290	9,161	44,284 (+1%)

L2 chain processing

Each column represents the number of blocks on the L2 chain where each block has 16 txs.

Metric	5 blocks	10 blocks
node_history_sync_time_in_ms	13,892 (-3%)	30,485 (-2%)
note_history_successful_decrypting_time_in_ms	2,295 (-3%)	4,665 (-2%)
note_history_trial_decrypting_time_in_ms	122	147 (+1%)
node_database_size_in_bytes	1,663,064 (+1%)	1,200,083
pxe_database_size_in_bytes	27,188	54,187

Circuits stats

Stats on running time and I/O sizes collected for every circuit run across all benchmarks.

Circuit	circuit_simulation_time_in_ms	circuit_input_size_in_bytes	circuit_output_size_in_bytes
private-kernel-init	43.3 (-1%)	56,577	14,745
private-kernel-ordering	21.3	20,137	8,089
base-rollup	850	631,605	811
root-rollup	39.0 (+3%)	4,072	1,097
private-kernel-inner	35.8 (-1%)	72,288	14,745
public-kernel-private-input	46.3 (-2%)	37,359	14,745
public-kernel-non-first-iteration	27.7 (-2%)	37,401	14,745
merge-rollup	0.899 (+2%)	2,592	873

Miscellaneous

Transaction sizes based on how many contracts are deployed in the tx.

Metric	0 deployed contracts	1 deployed contracts
tx_size_in_bytes	8,723	27,094