This PR ensures that `arcade.core` does not show up anywhere in "user
space". This is crucial for helping developers understand what objects
are safe to use, and helps maintain a good developer experience.
Specific changes:
- `ToolAuthorizationContext` and `ToolContext` are now visible via
`arcade.sdk`
- `ToolCatalog` is now visible via `arcade.sdk`
- `Toolkit` is now visible via `arcade.sdk`
- `config` is now visible via `arcade.sdk.config`
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