Requested changes from PR 29

[rob1997]

Summary

Addresses requested changes from PR #29 audit review. Implements pull-payment model for fees (claim vs. immediate transfer), subscription cancellation with prorated refunds, typo fix, zero-address validation, and additional tests. README and RPC API refs updated.

Changes

Asset

• Pull-payment model: Subscription payments held in the Asset contract; creator and registry claim fees via claimCreatorFee and claimRegistryFee instead of immediate transfer.
• Subscription struct: subscriptions now maps bytes32(id) to Subscription { startTime, endTime, subscriptionPrice }; uses nonces and EnumerableSet for subscribers.
• claimCreatorFee / claimRegistryFee: Creator claims via claimCreatorFee(subscriber); registry claims via claimRegistryFee(subscriber) on the Asset (registry calls it via claimRegistryFee(assetId, subscriber)).
• Subscription cancellation: cancelSubscription() allows users to cancel and receive prorated refund. revokeSubscription (owner) also triggers prorated refund.
• Typo fix: onlyRegsitryOrOwner → onlyRegistryOrOwner.
• Zero-address validation: Constructor reverts on _owner == address(0) or _tokenAddress == address(0).

AssetRegistry

• getFees: Added getFees(uint256 _value) returning (creatorFee, registryFee).
• claimRegistryFee: Registry owner can call claimRegistryFee(assetId, subscriber) to pull registry share.
• Renames: viewSubscription(bytes32) → viewMySubscription(bytes32), getSubscription(bytes32) → getMySubscription(bytes32).

Interfaces

• IAsset, IAssetRegistry updated for new functions and renames.

Tests

• Revoke, cancel, claim flows; negative tests; hardcoded assertions where appropriate; claimRegistryFee tests.

Documentation

• README updated with new flows, RPC API reference.
• registries_*.json updates.

[sqhell]

totalFeeShare can become zero if divided by zero
Add require(totalFeeShare > 0) after updating fee shares, or validate individual shares.

[sqhell]

claimCreatorFee and claimRegistryFee track separate claimedAt timestamps and compute fees using current fee shares (not the shares at subscription time)

users could set high register fee and drain balance.

the old design didn't have this issue as it computed and transferred fee splits at subscription time.

to fix: Store fee shares in the Subscription struct at subscribe time and use those for claims, and use single claimedAt. Make sure fee share changes only affect future subscriptions, so users aren't setting fees very high then returning normal to be able to drain the contract

[rob1997]

Yep, nice catch!

[rob1997]

already merged (deadlines...) but will fix