optimize: Use Smallvec

[aawsome]

Optimize BlobLocations for the case that this contains only a single blob - which can be ofthen the case.
In this case, this PR reduces memory allocations and size.

This affects the restore, prune and copy command.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 52.7%. Comparing base (d8abf46) to head (45a28be).

Additional details and impacted files

Files with missing lines	Coverage Δ
crates/core/src/blob.rs	70.5% <100.0%> (ø)
crates/core/src/commands/restore.rs	44.2% <100.0%> (+0.3%)	⬆️

... and 28 files with indirect coverage changes

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