## Description
Create a wrapper struct that provides a `Fetch(ctx, name) (Stream, error)` function that always returns `ErrNotFound`. A future PR is going to expand the `RestoreCollection` interface to include that function and I wanted to reduce the amount of chaff that would come out of it
This PR just creates the wrapper and moves `ErrNotFound` from the kopia package to `data` package to avoid import cycles
## Does this PR need a docs update or release note?
- [ ] ✅ Yes, it's included
- [ ] 🕐 Yes, but in a later PR
- [x] ⛔ No
## Type of change
- [x] 🌻 Feature
- [ ] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [x] 🤖 Test
- [ ] 💻 CI/Deployment
- [ ] 🧹 Tech Debt/Cleanup
## Issue(s)
* #1944
## Test Plan
- [ ] 💪 Manual
- [x] ⚡ Unit test
- [ ] 💚 E2E
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