ep: Only report shown once prediction is previewed in subtle mode (#52362)
Ben Kunkle
created
## Context
We currently mark the current prediction as "shown" when the subtle mode
indicator appears. This doesn't really make sense. We make an effort
elsewhere to differentiate between a user rejecting a prediction that
they viewed vs. never saw in order to compute accurate metrics.
## Self-Review Checklist
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- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable
Release Notes:
- N/A or Added/Fixed/Improved ...