Increase default chunk size for async request

.changes/next-release/bugfix-AWSSDKforJavav2-8d76030.json

@@ -0,0 +1,6 @@
+{
+    "type": "bugfix",
+    "category": "AWS SDK for Java v2",
+    "contributor": "",
+    "description": "Increased the default chunk size from 16KB to 128KB for async trailer-based checksum data transfers when using a custom legacy signer"
+}

core/sdk-core/src/main/java/software/amazon/awssdk/core/HttpChecksumConstant.java

@@ -42,7 +42,7 @@ public final class HttpChecksumConstant {
     /**
      * Default chunk size for Async trailer based checksum data transfer*
      */
-    public static final int DEFAULT_ASYNC_CHUNK_SIZE = 16 * 1024;
+    public static final int DEFAULT_ASYNC_CHUNK_SIZE = 128 * 1024;
 
     private HttpChecksumConstant() {
     }

core/sdk-core/src/test/java/software/amazon/awssdk/core/async/ChecksumCalculatingAsyncRequestBodyTckTest.java

@@ -20,7 +20,7 @@ public class ChecksumCalculatingAsyncRequestBodyTckTest extends PublisherVerific
     private static final int MAX_ELEMENTS = 1000;
     private final FileSystem fs = Jimfs.newFileSystem(Configuration.unix());
     private final Path rootDir = fs.getRootDirectories().iterator().next();
-    private static final int CHUNK_SIZE = 16 * 1024;
+    private static final int CHUNK_SIZE = 128 * 1024;
     private final byte[] chunkData = new byte[CHUNK_SIZE];
 
     public ChecksumCalculatingAsyncRequestBodyTckTest() throws IOException {