`cves` and `first_seen_at` added to Occurrences endpoint

Occurrences API Endpoint

Added two new fields to the Occurrences API endpoint to provide additional vulnerability information and timing data.

New fields added:

• cves: List of Common Vulnerabilities and Exposures (CVE) identifiers associated with the occurrence.
• first_seen_at: Timestamp indicating when the vulnerability was first detected.

For more information, see the API documentation for occurrences.