fix(pubsub): make process span current during receiveMessage()

[irock]

The subscribe process span is created but never set as the current context before calling MessageReceiver.receiveMessage(). This means user code inside the callback cannot create child spans under the process span, and downstream calls are not parented correctly.

Wrap the receiveMessage() calls in MessageDispatcher with Span.makeCurrent() so Context.current() contains the process span during user code execution. Add a getter for the process span on PubsubMessageWrapper and a test verifying child span parenting.

edit:

Assuming topic A & B, and a subscriber A on topic A, the intention is that this change will result in spans to have a hierarchy similar to the the following:

parent
└── topic A publish
    └── subscription A subscriber
        └── subscription A user code
            └── topic B publish

What we are currently seeing is the following:

parent
└── topic A publish
    ├── subscription A subscriber
    └── subscription A user code
      └── topic B publish

[gemini-code-assist]

Code Review

This pull request integrates OpenTelemetry tracing into the message dispatching process. Specifically, it ensures that the subscription process span is set as the current scope when receiving and processing Pub/Sub messages. A new unit test has also been added to verify this behavior. The review feedback suggests simplifying the try-with-resources statement by using null instead of Scope.noop(), which is more idiomatic in Java and avoids unnecessary API dependencies.

[gemini-code-assist]

In Java, a try-with-resources statement gracefully handles a null resource by doing nothing (no close() is called and no exception is thrown). We can simplify this by using null instead of Scope.noop(), which avoids the dependency on the Scope.noop() API and is more idiomatic.

Suggested change

	try (Scope ignored = processSpan != null ? processSpan.makeCurrent() : Scope.noop()) {
	try (Scope ignored = processSpan != null ? processSpan.makeCurrent() : null) {

[irock]

I believe the library is targeting Java 8, where a try-with-resources with a null resource will throw.

[irock]

Added some more context to the description.

[michaelpri10]

/gcbrun

[irock]

Thanks @michaelpri10 ! Is there anything else I need to do to get the PR merged? The "multi-approvers" check is failing for some reason.

[michaelpri10]

Added @blakeli0 as another reviewer to get multi-approval. After that, I think this PR should be ready to be merged.

[irock]

@michaelpri10 Looks like one more approval is needed :)

[phantasia15]

Hi! Just checking in—is there any chance this PR could be merged soon? I'm looking forward to using it.