Modernize project

[jodal]

• Update readme and docs
• Switch from setuptools to poetry
• Add .tool-versions for use with asdf or rtx
• Move the Read The Docs config into the repo
• Replace tox with nox
• Switch from Circle CI to GitHub Actions
• Run ruff format
• Run ruff --fix
• Fix exception lints
• Fix type annotation lints
• Fix date lints
• Ignore docstring lints
• Fix dict type annotations
• Add type annotations for dependencies
• Fix type annotations
• Make __all__ exports static and internal modules private

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