feat: add Tracking API

[MaelRB]

This PR

• Add Tracking API following OpenFeature specifications
• Every requirement from tracking has been developed
• No breaking change

Related Issues

Fixes 1234523

[gemini-code-assist]

Summary of Changes

Hello @MaelRB, 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 significantly enhances the OpenFeature Swift SDK by integrating the Tracking API. This feature allows developers to associate user actions and application states with feature flag evaluations, which is vital for robust experimentation and collecting telemetry. The changes introduce new core components for tracking, seamlessly integrate them into existing client and provider interfaces without breaking changes, and ensure that evaluation contexts are correctly merged for comprehensive data capture during tracking events.

Highlights

• Tracking API Implementation: The OpenFeature Swift SDK now includes a comprehensive Tracking API, fully adhering to the OpenFeature specifications for associating user actions with feature flag evaluations.
• New Protocols and Structures: Introduced Tracking and TrackingEventDetails protocols, along with the ImmutableTrackingEventDetails struct, to define and manage tracking event data.
• Client and Provider Integration: The Client protocol now conforms to Tracking, and OpenFeatureClient has been extended with track methods. The FeatureProvider protocol includes a new track method with a default no-op implementation for extensibility.
• Evaluation Context Merging: Enhanced OpenFeatureClient with logic to merge API-level and invocation-level evaluation contexts when reporting track events, ensuring comprehensive context capture.
• Documentation and Tests: The README.md has been updated to reflect the availability of the Tracking API with code examples. New unit tests have been added to validate the tracking functionality, context merging, and the ImmutableTrackingEventDetails struct.

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[gemini-code-assist]

Code Review

This pull request introduces the Tracking API, aligning the Swift SDK with the OpenFeature specification. The changes include new protocols (Tracking, TrackingEventDetails), concrete implementations (ImmutableTrackingEventDetails), and updates to the Client and FeatureProvider to support tracking events. The implementation is well-structured, with good separation of concerns and comprehensive test coverage for the new functionality. I've identified a potential issue in the context merging logic and a couple of areas for minor code simplification. Overall, this is a great addition to the SDK.

[beeme1mr]

Hey @MaelRB, thanks for the PR! Could you please sign off on your commits? It's a requirement from the CNCF because it signifies that you're willing and able to donate this code.

Instructions for signing previous commits can be found here. Thanks!

[beeme1mr]

Approving from an OpenFeature spec perspective, thanks.