Remove TaskTransform

[lukesteensen]

The current TaskTransform trait has a number of downsides:

• It's fundamentally tied to our async runtime
• It's rather complicated for contributors to understand
• Because it provides virtually no constraints on the implementation, we can't make any assumptions about what it will do when running it
• It has fallen behind on features like multiple outputs, without any clear path for how to add them

Luckily, almost all of the transforms currently implemented via TaskTransform could be written as something much simpler. This issue represents the work to transition those transforms to simpler abstractions that don't have the same downsides, either via existing traits or new ones designed for their needs.

As part of this work, especially if new types of transforms are added, we should try to completely unify the topology's view of transforms (similar to how FunctionTransform is run as a SyncTransform today) to remove the current duplication across types. Something like lua's RuntimeTransform could be a model for this, while we continue to offer contributors simpler options for the actual implementation.