Instead of modeling it as pause/resume, events are a good model here after all.

• You can await an event by name and send an event by name, in the simplest case
• You can also create an event ahead of time and pass around the ID.
• An event is only ever consumed by one step.
• It can be sent first or awaited first, and it'll have timestamps to know how long things took.
• You can send a full "result" payload - which will become the step's result - allowing erroring / canceling

Closes #122
Fixes #19
Fixes #25

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