The statig version was missing the per-node ExecutionState machine that
the bare version has. This commit adds it as a sub-module so its
generated `State` enum doesn't collide with the top-level PipelineMachine's
`State` enum.
Adds:
- ExecutionEvent enum (top-level, alongside PipelineEvent)
- mod execution { … } sub-module containing ExecutionMachine
- States: idle, pending, running, rate_limited, completed
- Cross-cutting `any` superstate that handles Stopped/Reset → Idle
- 6 new tests covering the happy path, rate-limit + resume, and
stop-from-anywhere via the superstate
Also adds a small note about how statig's `#[action]` entry/exit hooks
would replace the bare version's external EventBus pattern (without
implementing it — we'd pick one or the other based on whether side
effects should live inside or outside the state machine).
Test count: 11 → 17 (all passing).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Timmy
1707277bb7