Implement Closeable in QSCManager, document exception swallowing

Signed-off-by: owenhalpert <[email protected]>

src/main/java/org/opensearch/knn/index/memory/NativeMemoryCacheManager.java

@@ -109,6 +109,7 @@ private void initialize(NativeMemoryCacheManagerDto nativeMemoryCacheDTO) {
                 try {
                     cache.cleanUp();
                 } catch (Exception e) {
+                    // Exceptions from Guava shouldn't halt the executor
                     logger.error("Error cleaning up cache", e);
                 }
             };

src/main/java/org/opensearch/knn/quantization/models/quantizationState/QuantizationStateCache.java

@@ -83,6 +83,7 @@ private void buildCache() {
             try {
                 cache.cleanUp();
             } catch (Exception e) {
+                // Exceptions from Guava shouldn't halt the executor
                 log.error("Error cleaning up cache", e);
             }
         };

src/main/java/org/opensearch/knn/quantization/models/quantizationState/QuantizationStateCacheManager.java

@@ -9,10 +9,11 @@
 import lombok.NoArgsConstructor;
 import org.opensearch.knn.index.codec.KNN990Codec.KNN990QuantizationStateReader;
 
+import java.io.Closeable;
 import java.io.IOException;
 
 @NoArgsConstructor(access = AccessLevel.PRIVATE)
-public final class QuantizationStateCacheManager {
+public final class QuantizationStateCacheManager implements Closeable {
 
     private static volatile QuantizationStateCacheManager instance;
 
@@ -80,6 +81,7 @@ public void clear() {
         QuantizationStateCache.getInstance().clear();
     }
 
+    @Override
     public void close() throws IOException {
         QuantizationStateCache.getInstance().close();
     }