Built-in debugger

[mrwonko]

A good way to augment documentation in the #88 and visualize #22 executions could be a visual debugger that lets you step through the logic incrementally and explore alternative paths.

This would require annotations that could also be useful for OpenTelemetry-style "tracing".

This feels like something that would be valuable to have early, to help understand what I'm working with.

Halting mid-execution could be enabled through the use of coroutines, though a more general pure functional approach could help with multiverse time travel.