Fix lease extension expiry index transaction

[asg0451]

Fix expire_due_leases to accurately count processed leases by only incrementing for actual expirations, resolving the extend_existing_lease_updates_expiry_index test failure.

The expire_due_leases function was incorrectly incrementing its processed counter when cleaning up stale or superseded lease expiry index entries, rather than only when a lease genuinely expired and was requeued. This led to an overcount, causing the extend_existing_lease_updates_expiry_index test to fail.

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[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
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