Fix clippy lints in backfill and libraries tests

Keep `cargo clippy --tests` clean alongside the agentic-loop changes:
alias backfill's five-element setup() tuple as SetupFixture
(type_complexity) and build the single-library health map via
std::slice::from_ref instead of cloning (unnecessary clone-to-slice).
No behavior change.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/libraries.rs

@@ -1052,7 +1052,7 @@ mod tests {
             enabled: true,
             excluded_dirs: Vec::new(),
         };
-        let map = new_health_map(&[lib.clone()]);
+        let map = new_health_map(std::slice::from_ref(&lib));
 
         // First probe: empty dir, no prior data — Online.
         let s1 = refresh_health(&map, &lib, false);