Add warning publication and notification support

[ann-linh-mitre]

The CVE Program requires a centralized warning notification mechanism for broadcasting changes to CVE Record formats and validation rules, such as field deprecations.

Warnings are stored in a CVE Program registry and must be managed independently of CVE Record validation. Validation results must include the registered warnings without changing the record’s validation status.
Each warning contains:

• Message ID
• Notification message
• Notification details
• Schema path
• Date added
• Date updated
• Start date
• End date
• Priority

Definition of Done:

• Implement a centralized, JSON-backed warning notification registry.
• Store CVE Program warnings under src/registry/cve-program/warnings.json.
• Provide a public API for adding warnings independently of CVE Record validation.
• Validate warning data before saving it to the registry.
• Persist warnings across library executions.
• Include registered warnings in every Diagnostics validation result.
• Ensure warnings do not change the validation result’s valid, error, message, or details fields.
• Support warning priority and effective start/end dates.
• Provide an idempotent stub-warning script for local development.
• Export warning types and registry APIs from the package entry point.
• Document warning registration and validation-result behavior.
• Add tests covering persistence, registry reload, warning fields, and diagnostic serialization.