Which issue(s) does this change fix?

Why is this change necessary?

Customers using sam local invoke to test durable functions that are using callback operations need a way to know when their functions are suspended and waiting for a callback. Otherwise, the only other way to know is by querying the execution history (sam local execution history) and seeing a CallbackStarted and InvocationCompleted event. This is not the best user experience, and we should be prompting users to respond to pending callbacks immediately.

How does it address the issue?

This PR adds a callback handler which will prompt users to respond to pending callbacks. The prompts include success, fail, heartbeat or stopping the execution entirely. We create a new thread in the polling loop to prompt the user, so we can continue checking the execution state and history. If another process resolves the callback (e.g. you call sam local callback succeed from another session), the execution will continue.

What side effects does this change have?

None. Improved UX for callbacks in the local invoke loop.

Mandatory Checklist

PRs will only be reviewed after checklist is complete

• Review the generative AI contribution guidelines
• Add input/output type hints to new functions/methods
• Write design document if needed (Do I need to write a design document?)
• Write/update unit tests
• Write/update integration tests
• Write/update functional tests if needed
• make pr passes
• make update-reproducible-reqs if dependencies were changed
• Write documentation

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.