fix(l1,l2): inaccurate block execution metrics (#5108)

**Motivation**

Disaggregated block execution metrics are off because they count
accumulate rather than each process' times.
Given we treat them as parts of a single thing, e.g. later making a pie
chart of them, they should be counted as difference from the end of the
previous step, like we do in logs.

**Description**

Fix the subtractions.

Author: Oppen

crates/blockchain/blockchain.rs

@@ -581,8 +581,8 @@ impl Blockchain {
                 METRICS_BLOCKS.set_latest_block_gas_limit(gas_limit as f64);
                 METRICS_BLOCKS.set_latest_gigagas(throughput);
                 METRICS_BLOCKS.set_execution_ms(executed.duration_since(since).as_millis() as i64);
-                METRICS_BLOCKS.set_store_ms(stored.duration_since(since).as_millis() as i64);
-                METRICS_BLOCKS.set_merkle_ms(merkleized.duration_since(since).as_millis() as i64);
+                METRICS_BLOCKS.set_merkle_ms(merkleized.duration_since(executed).as_millis() as i64);
+                METRICS_BLOCKS.set_store_ms(stored.duration_since(merkleized).as_millis() as i64);
                 METRICS_BLOCKS.set_transaction_count(transactions_count as i64);
             );