fix(l2): handle better when producing an empty batch

[tomip01]

Motivation

The L2 was failing when trying to commit the first batch that was empty.
Inside produce_batch_from_block when doing the metrics we do:

let first_block_of_batch = last_added_block_number + 1;
// Rest of the code ...
let batch_size = (last_added_block_number - first_block_of_batch).try_into()?; // batch_size is an `i64`

This could end up in u64::max and failing the conversion because if there are no blocks in the batch we never do last_added_block_number += 1; inside the loop.

Description

• Handle the empty batch before doing the metrics
• Change produce_batch_from_block to return an Option<T>

[github-actions]

Lines of code report

Total lines added: 4
Total lines removed: 0
Total lines changed: 4

Detailed view

+--------------------------------------------+-------+------+
| File                                       | Lines | Diff |
+--------------------------------------------+-------+------+
| ethrex/crates/l2/sequencer/l1_committer.rs | 1077  | +4   |
+--------------------------------------------+-------+------+

[Copilot]

Pull Request Overview

This PR fixes a critical bug where the L2 sequencer would crash when attempting to commit an empty batch. The issue occurred during metrics calculation where an underflow would happen in the batch_size computation when no blocks were added to the batch.

• Changed prepare_batch_from_block to return Option<T> to handle empty batches gracefully
• Added early detection of empty batches before metrics calculation
• Updated the caller to properly handle the None case with pattern matching

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