Add Issue Events and Timeline functionality

[jordanpartridge]

Summary

Add support for GitHub Issue Events and Timeline to track the complete history of issue changes.

Features to Implement

Event Types

• Issue state changes (opened, closed, reopened)
• Label changes (labeled, unlabeled)
• Assignee changes (assigned, unassigned)
• Milestone changes (milestoned, demilestoned)

Event Operations

• List events for an issue
• Get specific event details
• Filter events by type
• Paginate through event history

GitHub API Endpoints

• GET /repos/{owner}/{repo}/issues/{issue_number}/events
• GET /repos/{owner}/{repo}/issues/{issue_number}/timeline
• GET /repos/{owner}/{repo}/issues/events/{event_id}

Priority

Medium - Valuable for advanced workflows and analytics