Fix Pydantic V3 deprecation warnings

[abrookins]

Problem

The codebase uses several Pydantic APIs that are deprecated in V2 and will be removed in V3:

• parse_raw() method (line ~1979) - should use model_validate_json()
• __fields__ attribute (lines ~1532, 1551, 2150) - should use model_fields class property
• Instance-level model_fields access (line ~1465) - should access from class, not instance

Impact

These deprecation warnings are confusing for users and the code will break when Pydantic V3 is released.

Related

• deprecation warnings #725 (user report of deprecation warnings)

Solution

Replace deprecated APIs with their V2/V3-compatible equivalents:

• cls.parse_raw() → cls.model_validate_json()
• cls.__fields__ → cls.model_fields
• self.model_fields → self.__class__.model_fields