Implement reset methods for XXHash checksum algorithms

[zoewangg]

Motivation and Context

XxHashChecksum.reset() previously threw UnsupportedOperationException, causing exception to be thrown from async streaming operations that use this checksum (no services use this today). This change implements reset() to properly close the old CRT resource and create a fresh instance. The root cause is that ChunkedEncodedPublisher resets all states including checksum in subscribe

aws-sdk-java-v2/core/http-auth-aws/src/main/java/software/amazon/awssdk/http/auth/aws/internal/signer/chunkedencoding/ChunkedEncodedPublisher.java

Lines 91 to 92 in 049935f

	public void subscribe(Subscriber<? super ByteBuffer> subscriber) {
	resetState();

Additionally, HttpChecksumCalculationTest relied on Mockito mocks with manual ArgumentCaptor wiring. This refactors it to use MockSyncHttpClient/
MockAsyncHttpClient from service-test-utils, and adds full request body verification for streaming checksum trailer tests.

Modifications

• XxHashChecksum: Implement reset() — closes the existing XXHash CRT resource and reinitializes
• XxHashChecksumTest: Replace reset_throwsUnsupportedOperationException with reset_allowsReuseOfChecksum
• HttpChecksumCalculationTest: Rewrite to use MockSyncHttpClient/MockAsyncHttpClient, add complete chunked body assertions for both sync and async streaming paths, add xxhash and sha256 test cases to checksumInHeaderRequiredParams
• MockAsyncHttpClient: Always capture streaming payload via ByteArrayOutputStream, return CompletableFuture that completes after payload capture, remove
  unused setAsyncRequestBodyLength

Testing

• Updated unit tests for XxHashChecksum.reset() behavior
• HttpChecksumCalculationTest now verifies exact chunked body content including trailer checksum values for all algorithms (CRC32, CRC32C, SHA1, SHA256,
  XXHASH3, XXHASH64, XXHASH128)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Checklist

• I have read the CONTRIBUTING document
• Local run of mvn clean install -pl :{module} succeeds for affected modules
• My code follows the code style of this project
• My change requires a change to the Javadoc documentation
• I have updated the Javadoc documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed
• I have added a changelog entry

License

• I confirm that this pull request can be released under the Apache 2 license

[zoewangg]

Removed this because MockAsyncHttpClient now always captures the streaming request payload, so pre-configuring the expected body length is no longer needed.

[zoewangg]

We should technically call request.subscription(1) here, but it'd trigger a bug in InMemoryPublisher that causes the request to hang. I'll fix it later. This shouldn't cause any real issues though since InMemoryPublisher only invokes onNext once.

[zoewangg]

Added no-api-surface-area-change because it's an internal API and it's not used by any service clients today

[sonarqubecloud]

Quality Gate failed

Failed conditions
28.6% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud

[github-actions]

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