Global and Client API

[NeaguGeorgiana23]

This PR

Adds the logic for GlobalAPI and ClientAPI.

Related Issues

Fixes #29 and #34

[gemini-code-assist]

Summary of Changes

Hello @NeaguGeorgiana23, 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 the OpenFeature C++ SDK by introducing the ClientAPI and OpenFeatureAPI components. The OpenFeatureAPI serves as a global singleton for managing feature providers and their lifecycle, including initialization and shutdown, while the ClientAPI provides the primary interface for applications to evaluate feature flags and manage client-specific evaluation contexts. The changes also streamline the core OpenFeature interface and enhance the robustness of provider management by ensuring a consistent default state after system shutdown.

Highlights

• Core API Introduction: New ClientAPI and OpenFeatureAPI classes are introduced, forming the foundation of the OpenFeature C++ SDK.
• API Interface Refinement: The OpenFeature interface is updated, removing SetProviderAndWait overloads with timeouts and adding const qualifiers to several getter methods for better immutability.
• Provider Management Enhancements: The ProviderRepository now ensures that after a Shutdown operation, the system gracefully resets to a default NoopProvider in a ready state.
• Build System Updates: openfeature/BUILD and test/BUILD files are updated to include the new API components and their corresponding unit tests.
• Comprehensive Unit Tests: New test files (client_api_test.cpp, openfeature_api_test.cpp) are added to validate the functionality of the new API classes, covering singleton behavior, provider management, and asynchronous operations.

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[gemini-code-assist]

Code Review

This pull request introduces the ClientAPI and OpenFeatureAPI implementations, which is a significant step forward. However, the current changes include several critical issues that need to be addressed before this can be merged. These issues include a circular dependency in the build configuration, incorrect handling of the singleton pattern which will lead to compilation errors and potential memory corruption, and a race condition on the evaluation context. I've also pointed out a few other issues related to correctness and maintainability, such as an incorrect include guard, a missing override specifier, flawed logic in context merging, and an outdated test. My review provides detailed feedback and suggestions for each of these points.

[oxddr]

Please rename this PR so the title matches the content.

[NeaguGeorgiana23]

This PR was splitted in smaller ones. See: Global Context Manager, Client API and Global API