Use `pydantic` effectively

[EarlMilktea]

Is your feature request related to a problem? Please describe.

Currently pydantic validations are sorely used to validate types, which can be elided assuming type annotations are respected.

Describe the feature you'd like

• Use pydantic to check additional constraints not manifested in type annotations, otherwise remove it
• Remove BaseModel inheritance to avoid unnecessary automatic validations
• Define simple models and use them manually