Refactor get_task_function

[pedro-psb]

We have a complex setup going on.

Task Type | Context Type | Immediate || Adapter Required | Notes                                               |
----------|--------------|-----------||------------------|-----------------------------------------------------|
Async     | Async        | Yes       || No               | Direct execution                                    |
----------|--------------|-----------||------------------|-----------------------------------------------------|
Async     | Sync         | Yes       || Yes              | Async task in sync context needs adapter            |
Async     | Sync         | No        || Yes              | Async task in sync context needs adapter            |
Sync      | Sync         | No        || No               | Direct execution                                    |
----------|--------------|-----------||------------------|-----------------------------------------------------|
Sync      | Sync         | Yes       || Invalid          | Immediate requires async task                       |
Sync      | Async        | Yes       || Invalid          | Immediate requires async task                       |
Sync      | Async        | No        || Invalid          | Always executed in sync context (worker)            |
Async     | Async        | No        || Invalid          | Always executed in sync context (worker)            |

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All the logic was being handled in a single function with lots of conditional branches, which was hard to read and reason about. Tthis splits it in more digestable auxiliary functions and tries to make the logic more clear.

[pedro-psb]

There is nothing really async in this. It's just to enforce it's supposed to be run in async context.