[Feature Request] Implement Subgraph to Track Payment Channels

[pali101]

Description

Currently, the SDK does not provide a way to fetch all active payment channels for a user (payer or merchant). Instead of modifying the smart contract, we can use The Graph to index payment channels and query them efficiently.

Proposed Solution

1. Deploy a subgraph
   • Index ChannelCreated, ChannelRedeemed, and ChannelClosed events.
   • Store channels between payers and merchants.
2. Update the SDK
   • Add a function to query the subgraph for a list of open channels by payer.
   • Add a function to query the subgraph for a list of open channels with merchant.
3. Expose API for Frontend
   • Allow frontends to easily fetch all open channels for a user without scanning on-chain data.

Benefits

• Cheaper & Faster - No additional gas costs for storage, and queries are nearly instant.
• Better User Experience - Fetch all active channels in a single GraphQL query.
• Scalable - Easily extendable to add more analytics, filtering, or historical data.