Some of the misc issues were found with mypy. Not adding it to dev deps for now as it complains about missing types in libraries and does not honor noqa where we need it (non-literal TypedDict keys).
Allows permanently configuring itch-dl with an API key and other things in the future. Adds a new dependency, Pydantic, to validate the config.
Wooo, someone wants to use this! Let's make it less embarrassing.
