feat: Implement data models for deprecation entries

[leblancfg]

Summary

• Implements Pydantic models for deprecation data handling
• Adds RSS feed generation capabilities
• Provides comprehensive validation and type safety

Changes

• RawDeprecation model: Handles scraped data with validation for providers, dates, and URLs
• DeprecationEntry model: Business logic layer with RSS serialization and active status checking
• DeprecationFeed model: Manages collections of entries and generates RSS XML output
• Comprehensive tests: Full test coverage using pytest-describe pattern

Implementation Details

• All models use Pydantic v2 with strict type hints
• Support for partial data (only provider and model_name required)
• Date validation ensures retirement_date > deprecation_date when both present
• RSS generation using feedgen library
• Historical tracking support with created_at/updated_at timestamps

Testing

• 32 tests passing
• Type checking with mypy - no errors
• Linting with ruff - all checks passed

Closes #2