[BUG] The order of opIndexes are not guaranteed to be incremental during mutable segment switch

[koculu]

Recently, the internal operation index (op index) per mutable segment was exposed to simplify the replication process. See Issue #93 for more details.

Initially, the op indexes were designed to increment only within the scope of their respective mutable segment. Consequently, when switching between mutable segments, the op index order is not guaranteed to remain incremental.

To ensure consistency, improve the mutable segment switch process to guarantee that the op index order remains incremental across segment transitions.