Rename types.py fields from camelCase to snake_case #1738

Summary

Rename fields in the types module from camelCase to snake_case to follow Python naming conventions.

Motivation

• Python convention is snake_case for attributes and variables
• Current camelCase naming was inherited from the JSON schema / TypeScript origins
• Makes the API feel more Pythonic

Migration

• Use Pydantic field aliases to maintain wire compatibility
• Add deprecation warnings for camelCase access during transition period

Related

• Part of broader types.py restructuring for v2
• Remove Pydantic RootModels from types module #1737 - Remove RootModels

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