fix(l2): correctly accumulate operations counts in in-memory rollup store

[Fibonacci747]

Motivation

The in-memory rollup store is used in L2 components that expose metrics about transactions, privileged transactions and messages. These metrics depend on the global counters exposed by get_operations_count. However, the in-memory implementation of update_operations_count was not updating the underlying state at all, so the counters always stayed at zero. This silently broke L2 metrics when the in-memory backend is used and also made its behavior diverge from the SQL backend.

Description

This change fixes the in-memory implementation of StoreEngineRollup::update_operations_count so that it mutates the operations_counts array inside StoreInner instead of working on a local copy. As a result, subsequent calls to get_operations_count now return the accumulated values, matching the semantics of the SQL backend. A small async unit test was added to in_memory.rs to verify that multiple updates correctly accumulate and are reflected in the result of get_operations_count.