perf(linter): reduce iterations when collecting directories for nested configs

apps/oxlint/src/lint.rs

@@ -445,7 +445,10 @@ impl LintRunner {
             while let Some(dir) = current {
                 // NOTE: Initial benchmarking showed that it was faster to iterate over the directories twice
                 // rather than constructing the configs in one iteration. It's worth re-benchmarking that though.
-                directories.insert(dir);
+                let inserted = directories.insert(dir);
+                if !inserted {
+                    break;
+                }
                 current = dir.parent();
             }
         }