feat(observability): add no-op implementation of tracing

[diegomarquezp]

This PR introduces a basic implementation for tracing in GAX. This is a minimal no-op placeholder intended to establish the project's architecture before adding functional tracing logic.

Changes:

• New Tracing Components:

  • new classes such as TracingRecorder mimic the structure of the metrics counterpart.

• Feature Flag Implementation:

  • Added TracingUtils to manage the GOOGLE_CLOUD_ENABLE_TRACING feature flag. Tracing is disabled by default and can be enabled via an environment variable or system property.
  • Updated TracingTracerFactory to respect this flag, returning a no-op BaseApiTracer when tracing is disabled.

Note on Implementation:

The newTracer method in TracingTracerFactory and the tracing components themselves are currently implemented as placeholders. This PR focuses on establishing the basic structure and configuration mechanisms; actual tracing logic and attribute propagation will be implemented in subsequent phases.

How to enable tracing:

To enable the tracing infrastructure, set the following environment variable or system property to true:
GOOGLE_CLOUD_ENABLE_TRACING=true

[gemini-code-assist]

Summary of Changes

Hello @diegomarquezp, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request lays the groundwork for distributed tracing within the gax-java library by introducing a new, extensible tracing framework. It provides the core interfaces and classes necessary to record RPC lifecycle events, with an initial no-op implementation that leverages OpenTelemetry. The changes also include a feature flag to control tracing activation and a set of tests to ensure proper functionality, paving the way for more detailed observability of client-side operations.

Highlights

• New Tracing Framework: Introduced a new tracing framework with a TracingRecorder interface, designed to be framework-agnostic for recording RPC lifecycle events.
• OpenTelemetry Integration: Added an OpenTelemetryTracingRecorder class, providing an initial OpenTelemetry-specific implementation for the TracingRecorder interface.
• Tracing Tracer and Factory: Implemented TracingTracer and TracingTracerFactory to integrate the new tracing capabilities into the existing ApiTracer system, allowing for the creation and management of trace spans.
• Feature Flag for Tracing: Included TracingUtils to manage tracing enablement, allowing users to activate or deactivate tracing via the GOOGLE_CLOUD_ENABLE_TRACING system property or environment variable.
• Comprehensive Testing: Added new unit tests for the tracing components and an integration test in ITOtelMetrics to validate the tracing feature flag's behavior.

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[gemini-code-assist]

Code Review

This pull request introduces a no-op implementation for tracing, which is a great first step towards full observability. The new classes and interfaces for tracing are well-structured. I've found a few areas for improvement, mainly concerning code correctness in a test setup, and some opportunities to improve encapsulation and prepare for the full implementation by aligning more closely with the existing metrics implementation. My comments provide specific suggestions for these points.

[gemini-code-assist]

The tracingRecorder field is protected and mutable. Since it's initialized in the constructor and not expected to be changed by subclasses, it should be private final to ensure immutability and proper encapsulation.

Suggested change

	protected TracingRecorder tracingRecorder;
	private final TracingRecorder tracingRecorder;

[diegomarquezp]

@blakeli0 https://github.com/googleapis/sdk-platform-java/pull/2403/files#diff-fdc1dfb7a2b23501ab66d8e37f0aedc5ca87489d845479734f583773bab0a51a shows that the metrics counterpart also has the recorder as protected. Do you know if we intend to have these classes extended at some point? I imagine a new metrics sdk may require a sub class.

[sonarqubecloud]

Quality Gate passed for 'gapic-generator-java-root'

Issues
4 New issues
0 Accepted issues

Measures
0 Security Hotspots
84.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[sonarqubecloud]

Quality Gate passed for 'java_showcase_integration_tests'

Issues
4 New issues
0 Accepted issues

Measures
0 Security Hotspots
92.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[diegomarquezp]

WIP as there are pending design decisions for the feature flag.