fixes #13428

This PR ensures the app variable is available when the server pushes chunks to the client to decode custom data types as they stream in. This fixes streaming for split and single apps by wrapping the code that references app after an import statement, and providing the correct global variable for inline apps.

An additional test suite for inline apps has also been added since none existed before. However, feel free to remove it if it's too much just to test inline apps.

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