Remove old task runners and futures modules

[desertaxle]

Moves new_task_runners and new_futures to task_runners and futures, respectively. Deletes old task_runners and future modules.

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[desertaxle]

This fixes the failures we've been seeing with the benchmarks job

[abrookins]

Looks good to me. 👍

[abrookins]

One question I have that isn't directly about this PR but that it reminded me of is why did we remove the SequentialTaskRunner? I get that it doesn't serve a purpose in production code, but I thought it was there to help people write tests for their flows easier. 🤔

[desertaxle]

One question I have that isn't directly about this PR but that it reminded me of is why did we remove the SequentialTaskRunner? I get that it doesn't serve a purpose in production code, but I thought it was there to help people write tests for their flows easier. 🤔

I removed it because the SequentialTaskRunner breaks the model of .submit triggering a non-blocking execution of a task. I would suggest the ThreadPoolTaskRunner to users if they want to test their flows since it maintains non-blocking execution, but you can run it locally without any dependencies.