## Description
Add a function to fetch a file from the collection synchronously. This will help avoid data dependencies on the restore path created by splitting item information across multiple kopia files
Fetch function is currently unoptimized, though deeper analysis of memory footprint should be done before changing
Viewing by commit will help reduce chaff from updating tests to comply with the new interface
## 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
- [ ] 🤖 Test
- [ ] 💻 CI/Deployment
- [ ] 🧹 Tech Debt/Cleanup
## Issue(s)
* #1535
## Test Plan
- [ ] 💪 Manual
- [x] ⚡ Unit test
- [ ] 💚 E2E
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