fix: implement GraphQL pagination to fetch all PRs and issues

[Aryan-Verma-999]

Fix: Implement GraphQL Pagination for Complete Data Fetching

Fixes #3

Problem

The script only fetched the first 100 PRs/issues per repository, missing contributions in larger repos.

Solution

• Implemented cursor-based pagination using pageInfo { hasNextPage, endCursor }
• Added early termination when hitting items older than startDate (optimization)

Testing

• Verified against 39 RocketChat repositories
• Rocket.Chat now shows 115+ PRs (previously capped at 100)

Happy to make any changes if needed!