Use published car reader in Old Faithful worker

[augustin-cheron]

What changed

• resolve the Old Faithful get-block Worker's of-car-reader dependency from crates.io at exactly 0.2.0
• resolve the local of-slot-ranges helper against the same registry package so the Worker has one car-reader instance
• lock the published archive checksum

Why

The Worker was built from the repository path even after of-car-reader 0.2.0 was published. This change makes the deployed artifact consume the immutable crates.io release and prevents a second local copy through of-slot-ranges.

Verification

• cargo check -p old-faithful-get-block --target wasm32-unknown-unknown
• cargo test --locked -p old-faithful-get-block --lib (10 passed)
• cargo test --locked -p of-slot-ranges --all-targets (49 passed)
• worker-build --release .
• dependency graph contains one registry of-car-reader 0.2.0 with checksum bc7ecea28523a45ff40dc48ec607454edc7566d59ba8b151d82b87c9fd5e895d