- Modified currency__rate from integer to float in fiverr_listings, fiverr_gigs, fiverr_seller_profiles
- Added stats_processed_at and stats_processed_status to fiverr_listings
- Added fiverr_listings_stats table migration
- Added stats helper methods to FiverrJsonImporter:
  - getSellerLevelNumeric()
  - calculateSellerLevelStats()
  - extractFacetCount()
  - categorizeGigType()
  - computeListingsStatsRow()