[TH2-5204] added DropDuplicatesPredicate.

cradle-core/src/main/java/com/exactpro/cradle/BookInfo.java

@@ -226,7 +226,7 @@ public Iterator<PageInfo> getPages(@Nullable Instant leftBoundTimestamp,
         }
         return builder.build()
                 .flatMap(epochDay -> getPageInterval(epochDay).stream(leftTimestamp, rightTimestamp, order))
-                .distinct()
+                .filter(new DropDuplicatesPredicate<>())
                 .iterator();
     }
 
@@ -472,6 +472,22 @@ private interface IPageInterval {
         Stream<PageInfo> stream(Instant leftBoundTimestamp, Instant rightBoundTimestamp, Order order);
     }
 
+    /**
+     * This is stateful predicate because it holds previous checked element in class variable.
+     * You use it to drop duplicated elements in ordered stream without parallel mode.
+     */
+    private static final class DropDuplicatesPredicate<T> implements Predicate<T> {
+        private T previous = null;
+        @Override
+        public boolean test(T t) {
+            if (Objects.equals(previous, t)) {
+                return false;
+            }
+            previous = t;
+            return true;
+        }
+    }
+
     private static final class EmptyPageInterval implements IPageInterval {
 
         @Override