[FSSDK-11544] Parsing holdout configuration from datafile + project config holdout impl.

[junaed-optimizely]

Summary

Datafile Parsing to support holdout + ProjectConfig holdout change

Test plan

Tests have been added to support the changes

Issues

FSSDK-11544
FSSDK-11545

[Copilot]

Pull Request Overview

Implements holdout functionality for the Optimizely SDK by adding datafile parsing support and project configuration integration. This enables holdout experiments that can be applied globally or targeted to specific feature flags.

• Added comprehensive holdout entity model with flag inclusion/exclusion logic
• Introduced holdout configuration manager for efficient flag-to-holdout relationship mapping
• Extended project configuration interface to support holdout operations and queries

Reviewed Changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
OptimizelySDK/Utils/HoldoutConfig.cs	Core holdout configuration manager with caching and flag relationship logic
OptimizelySDK/Entity/Holdout.cs	Complete holdout entity implementation with audience and variation support
OptimizelySDK/Entity/IExperimentCore.cs	Shared interface for common experiment/holdout functionality
OptimizelySDK/Entity/ExperimentCoreExtensions.cs	Extension methods for shared experiment/holdout operations
OptimizelySDK/Entity/Experiment.cs	Updated to implement IExperimentCore interface
OptimizelySDK/ProjectConfig.cs	Added holdout-related interface methods
OptimizelySDK/Config/DatafileProjectConfig.cs	Integrated holdout parsing and configuration management
Various project files	Added new entity and utility files to compilation
Test files	Comprehensive test coverage for holdout functionality

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[mikechu-optimizely]

I've reviewed and provided comments around performance and consistency. I do not see any security problems. I'm providing a non-blocking approval but suggest consideration of the comments from me and Copilot. Good work. Welcome to C#. 😁

[muzahidul-opti]

Updated architecture looks good to me.
Leave a comment to remove the duplicate logic.