[Feature] Implement GitHub "Access Check" Logic

**Title:** [Feature] Implement GitHub Repository Access Check Logic

### Description
We need a core function for the `watcher` service that checks if a user's wallet holds a valid (non-expired) SubNFT before adding them to a GitHub repo.

### Goal
Write a script in `apps/watcher` that queries the blockchain for an NFT's expiration date and returns a boolean.
