Replace pydantic.BaseSettings with simpler checks

[adrianeboyd]

Description

It would be difficult to maintain compatibility with both pydantic v1 and v2 with BaseSettings.

Types of change

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Checklist

• [x] I confirm that I have the right to submit this contribution under the project's MIT license.
• [x] I ran the test suite, and all new and existing tests passed.
• [x] My changes don't require a change to the documentation, or if they do, I've added all required information.