BSA for integration test (#2256)

Supports the full blocklist download cycle (download, diffing, diff-apply, and order-status reporting) and the refreshing of unblockable domains.

Submitted due to tight deadline. We will conduct post-submit review and refactoring.

common/src/main/java/google/registry/util/BatchedStreams.java

@@ -0,0 +1,43 @@
+// Copyright 2023 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.util;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.collect.Iterators.partition;
+import static com.google.common.collect.Iterators.transform;
+import static com.google.common.collect.Streams.stream;
+import static java.lang.Math.min;
+
+import com.google.common.collect.ImmutableList;
+import java.util.stream.Stream;
+
+/** Utilities for breaking up a {@link Stream} into batches. */
+public final class BatchedStreams {
+
+  static final int MAX_BATCH = 1024 * 1024;
+
+  private BatchedStreams() {}
+
+  /**
+   * Transform a flat {@link Stream} into a {@code Stream} of batches.
+   *
+   * <p>Closing the returned stream does not close the original stream.
+   */
+  public static <T> Stream<ImmutableList<T>> toBatches(Stream<T> stream, int batchSize) {
+    checkArgument(batchSize > 0, "batchSize must be a positive integer.");
+    return stream(
+        transform(partition(stream.iterator(), min(MAX_BATCH, batchSize)), ImmutableList::copyOf));
+  }
+}