schema_evolution.rs had two `#[allow(unused_imports)]` attributes hiding
over-broad top-level imports:
- `Schema` was imported at crate level but only used in test code
- `Arc` was imported at crate level but only used in test code
- `DataType` and `SchemaRef` were actually used (28 references) — the
allow on that line was cargo-culted.
Fix: drop the allows, move Schema + Arc into the #[cfg(test)] block
where they're actually used. The non-test build no longer imports
symbols it doesn't need. Test build still works because the imports
are now in the test module's scope.
Workspace warnings still at 0 (lib + tests). Net: -3 import lines
from crate scope, +2 into test scope.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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