Improve the `ContextPipeline.compose` API

[janbuchar]

• The current state (accepting an object with action and cleanup callbacks) is more of an MVP
  • type inference is less than optimal
  • it's a lot of writing
  • sharing some stuff between action and cleanup without making it part of the extended context is tricky
• Alternative A: Accept a function that will return a cleanup callback (similarly to useEffect in React)
• Alternative B: Accept an async generator that will yield the context extension and clean up afterwards (similarly to Pytest fixtures and to crawlee-python)
• Alternative C: Accept an instance of a class
• Relevant discussion https://apify.slack.com/archives/C02JQSN79V4/p1756468275920019