Fix HttpChecksumStage ordering and SIGNING_METHOD resolution for interceptors to pipeline migration

[S-Saranya1]

Motivation and Context

After moving auth scheme resolution to a pipeline stage, SIGNING_METHOD is computed too early — before SELECTED_AUTH_SCHEME has the resolved values. This causes HttpChecksumStage to skip adding trailing checksums for requests that need them (e.g., S3 PutObject with MRAP + old signer), because ENABLE_CHUNKED_ENCODING is null at computation time.

Modifications

• AmazonSyncHttpClient / AmazonAsyncHttpClient — Moved HttpChecksumStage to run after AuthSchemeResolutionStage and EndpointResolutionStage, so it reads SIGNING_METHOD after it's been recomputed.
• SdkInternalExecutionAttribute — Added SIGNING_METHOD_UPDATER callback attribute.
• AwsExecutionContextBuilder — Sets the SIGNING_METHOD_UPDATER callback that recomputes SIGNING_METHOD using resolveSigningMethodUsed() with the correct values.
• AuthSchemeResolutionStage — Invokes the SIGNING_METHOD_UPDATER callback after resolving the auth scheme, when ENABLE_CHUNKED_ENCODING is available on SELECTED_AUTH_SCHEME.

Testing

Verified with existing ChecksumReuseTest - all 6 tests pass including the previously failing MRAP + old signer case.

Screenshots (if appropriate)

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 install succeeds
• 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
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• My change is to implement 1.11 parity feature and I have updated LaunchChangelog

License

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

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