Implements Step 6.1 of the plan:
- Add edit_event() function in events/edit.py
- Store old version in event_revisions before editing
- Increment version on edit
- Update projections via revert/apply pattern
- Add EventNotFoundError and EventTombstonedError exceptions
Tested with:
- Unit tests for revision storage and version increment
- Fast-revert tests for FeedGiven/FeedPurchased events
- Unbounded replay tests for AnimalMoved events
- E2E test #5: Edit egg event 8→6 with stats verification
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
