Remove Pydantic RootModels from types module #1737

Summary

Remove the use of Pydantic RootModel wrappers in the types module where they add complexity without clear benefit.

Motivation

• RootModels add indirection that makes the types harder to work with
• Many of these could be replaced with simpler type aliases or direct types
• The types should ideally be generated from the spec, and RootModels complicate that path

Related

• Part of broader types.py restructuring for v2

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