add type annotations / hints

[g-k]

e.g. with dataclass or typeddict from the stdlib or if botocore provides types.

This would prevent issues and make it clearer what's being passed around.

We can try to infer types with https://monkeytype.readthedocs.io/en/latest/generation.html at a quick pass I didn't see an obvious way to invoke the frost CLI.

[hwine]

This ticket covers ways to update legacy code. For all new code, use of type hints is encouraged.