- fix overflow in miner reward distribution
- implement one-time upfront payment + monthly billing cycle
- ensure prepaid subscriptions are only charged after credits expire
- fix double billing edge case in marketplace pallet
- correct referral reward payout (now transferred to owner)

- add storage tracking in arion pallet:
  - hcfs file count & size
  - s3 file count & size
- add update function for storage metrics

- add whitelist address storage (sudo-controlled)
- add cancel_subscription:
  - users: mark inactive (retain storage)
  - validators: cleanup storage after file deletion