Run openserch asyn callbacks with parent context

[laurit]

https://develocity.opentelemetry.io/s/252w7o5o7ozza/tests/task/:instrumentation:opensearch:opensearch-java-3.0:javaagent:test/details/io.opentelemetry.javaagent.instrumentation.opensearch.v3_0.OpenSearchApacheHttpClient5TransportTest/shouldGetStatusAsyncWithTraces()?expanded-stacktrace=WyIwIl0&top-execution=1
Our instrumentations run callbacks with parent context not the context of the span that was create for the operation that triggered the callback.

[Copilot]

Pull request overview

This PR fixes the OpenSearch 3.0 async instrumentation to run user-attached callbacks with the parent context active, rather than the context of the OpenSearch span created for the operation. This aligns the behavior with other async instrumentations in the repository (e.g., Apache HTTP async client, Elasticsearch REST/transport, Vertx HTTP client) which all propagate the parent context to user callbacks.

Changes:

• Adds a wrapFuture helper that creates a new CompletableFuture wrapper ensuring the parent context is active when downstream callbacks execute.
• Updates test assertions in both AbstractOpenSearchTest and OpenSearchAwsSdk2TransportTest to expect the "callback" span to be parented to the root "client" span (index 0) instead of the OpenSearch operation span (index 1).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
instrumentation/opensearch/opensearch-java-3.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/opensearch/v3_0/OpenSearchTransportInstrumentation.java	Stores parentContext in AdviceScope, adds static wrapFuture method to wrap the returned future with parent context propagation
instrumentation/opensearch/opensearch-java-3.0/javaagent/src/test/java/io/opentelemetry/javaagent/instrumentation/opensearch/v3_0/AbstractOpenSearchTest.java	Updates async test to assert callback span is parented to the root span (index 0)
instrumentation/opensearch/opensearch-java-3.0/javaagent/src/test/java/io/opentelemetry/javaagent/instrumentation/opensearch/v3_0/OpenSearchAwsSdk2TransportTest.java	Same parent assertion fix for the AWS SDK transport variant