perf(billing): bound cycle close's previous-period lookup below the elapsed period

The covering usage_log period index added in 0441 has unique keys, so B-tree deduplication can't compress an entity's current period the way the old four-column index did, and max(billing_period_start) for the previous period walked every current-period entry first. The elapsed period starts before it ends, so bounding the start below it changes no answer and lets the scan skip the current period.

Author: waleedlatif1

apps/sim/lib/billing/cycle-close.ts

@@ -373,7 +373,11 @@ export async function closeElapsedBillingPeriod(
       and(
         eq(usageLog.billingEntityType, billingEntity.type),
         eq(usageLog.billingEntityId, billingEntity.id),
-        eq(usageLog.billingPeriodEnd, periodStart)
+        eq(usageLog.billingPeriodEnd, periodStart),
+        // The elapsed period starts before it ends; stating it lets the backward scan of the
+        // covering period index skip the current period's entries, which its unique keys can't
+        // deduplicate, instead of walking all of them to reach the previous period.
+        lt(usageLog.billingPeriodStart, periodStart)
       )
     )
   const expectedPrevStart = prevStamp?.start ?? minusOneInterval(periodStart, sub.billingInterval)