Fix Infinity validation in daysBetween

The function only checked for NaN, not Infinity. If the date string represented
an extreme date, getTime() could return Infinity, causing Math.round(Infinity)
to return Infinity.

Changed Number.isNaN() to Number.isFinite() to catch both NaN and Infinity.

Author: pavankumar-vh

common/src/util/reddit-freebuff-retention.ts

@@ -14,7 +14,7 @@ export type FreebuffRedditConversionPlan = {
 function daysBetween(fromDateKey: string, toDateKey: string): number {
   const from = new Date(`${fromDateKey}T00:00:00.000Z`).getTime()
   const to = new Date(`${toDateKey}T00:00:00.000Z`).getTime()
-  if (Number.isNaN(from) || Number.isNaN(to)) {
+  if (!Number.isFinite(from) || !Number.isFinite(to)) {
     throw new Error(`Invalid date key range: ${fromDateKey} -> ${toDateKey}`)
   }
   return Math.round((to - from) / DAY_MS)