Fix clippy manual_range_contains warnings

Use (0..k).contains(&label) instead of manual range checks

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: raphaelsty

src/algorithm.rs

@@ -325,7 +325,7 @@ mod tests {
 
         // All labels should be valid
         for &label in result.labels.iter() {
-            assert!(label >= 0 && label < 5);
+            assert!((0..5).contains(&label));
         }
     }
 

src/kmeans.rs

@@ -256,7 +256,7 @@ mod tests {
         assert_eq!(labels.len(), 100);
 
         for &label in labels.iter() {
-            assert!(label >= 0 && label < 8);
+            assert!((0..8).contains(&label));
         }
     }
 

tests/integration_tests.rs

@@ -155,7 +155,7 @@ fn test_basic_predict() {
 
     // All labels should be in valid range
     for &label in labels.iter() {
-        assert!(label >= 0 && label < 8, "Labels should be in range [0, k)");
+        assert!((0..8).contains(&label), "Labels should be in range [0, k)");
     }
 }