feat: Add comprehensive GitHub API rate limit handling

[michaelpiramanrique271-tech]

This PR adds robust rate limit handling for all GitHub API calls to improve reliability and prevent failures when approaching or exceeding API limits.

Changes:

• Add RateLimitInfo dataclass to parse and track rate limit state
• Add parse_rate_limit_headers() to extract rate limit info from responses
• Add is_rate_limited() to detect rate limiting (403/429 status codes)
• Add check_preemptive_rate_limit() for early warning when approaching limits
• Add wait_for_rate_limit_reset() with progress logging for long waits
• Integrate rate limit handling into get_github_user()
• Integrate rate limit handling into get_pull_request_file_changes()
• Integrate rate limit handling into get_github_graphql_query()

Benefits:

• Prevents validator failures during high API usage periods
• Automatic retry with proper wait times when rate limited
• Proactive warnings when approaching rate limits
• Better observability through detailed logging