chore: fix BlobReadSession ReadProjectionConfigs.asSeekableChannel() close() behavior (googleapis#3047)

Update SeekableChannel close() to only execute close logic once.

Author: BenWhitehead

google-cloud-storage/src/main/java/com/google/cloud/storage/ObjectReadSessionSeekableByteChannel.java

@@ -130,6 +130,9 @@ public boolean isOpen() {
 
   @Override
   public void close() throws IOException {
+    if (!open) {
+      return;
+    }
     try (IOAutoCloseable ignore1 = closeAlongWithThis;
         ReadableByteChannel ignore2 = rbc) {
       open = false;

google-cloud-storage/src/test/java/com/google/cloud/storage/ObjectReadSessionLifeCycleTest.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2025 Google LLC
+ *
+ * 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 com.google.cloud.storage;
+
+import static com.google.cloud.storage.TestUtils.assertAll;
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.storage.v2.Object;
+import java.io.IOException;
+import java.util.concurrent.atomic.AtomicInteger;
+import org.junit.Test;
+
+public final class ObjectReadSessionLifeCycleTest {
+
+  @Test
+  public void seekableChannel_closeOnlyExecutesOnce() throws Exception {
+
+    AtomicInteger sessionCloseCount = new AtomicInteger(0);
+    AtomicInteger closeAlongCount = new AtomicInteger(0);
+
+    ObjectReadSession session =
+        new ObjectReadSession() {
+          @Override
+          public Object getResource() {
+            return Object.getDefaultInstance();
+          }
+
+          @Override
+          public <Projection> Projection readAs(ReadProjectionConfig<Projection> config) {
+            return null;
+          }
+
+          @Override
+          public void close() throws IOException {
+            sessionCloseCount.getAndIncrement();
+          }
+        };
+    ObjectReadSessionSeekableByteChannel channel =
+        new ObjectReadSessionSeekableByteChannel(
+            session,
+            ReadAsSeekableChannel.INSTANCE,
+            session.andThen(closeAlongCount::getAndIncrement));
+
+    channel.close();
+    channel.close();
+    channel.close();
+
+    assertAll(
+        () -> assertThat(sessionCloseCount.get()).isEqualTo(1),
+        () -> assertThat(closeAlongCount.get()).isEqualTo(1));
+  }
+}