Implement Experiment Metadata Tracking for Realtime Config Updates

[tusharkhandelwal8]

This PR introduces experiment metadata tracking to the Remote Config Realtime Service. Previously, onConfigUpdate was only triggered if a parameter's value changed. With this change, the SDK now detects changes in A/B test assignments (experiments/variants) for specific parameters, even if their values remain identical.

Key Changes:

• Experiment Mapping: Added createExperimentsMap to pivot raw experiment data into a lookup table where config keys are the primary index.
• Enhanced Diffing: Updated the change detection logic in RCNConfigContent to compare active vs fetched experiment metadata using the affectedParameterKeys field.
• Asynchronous Safety: Integrated waitForDatabaseOperationQueue to ensure experiment payloads are fully loaded from the disk before performing diffing logic.

Validation / Testing Scenarios:

• Add/Remove Experiment: Verified that adding or removing an experiment from a config key flags that key as changed.
• Replace Experiment: Verified that switching a key from one experiment/variant to another triggers an update.
• New Parameter: Verified that a brand new parameter with an attached experiment is correctly identified as a changed key.
• Value Persistence: Confirmed that a change in variantId triggers an update even if the parameter value (e.g., "hello world") stays the same.

Testing on Sample iOS App: Link

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[ashish-kothari]

LGTM!

[paulb777]

Please address the CI failures

[ncooke3]

/gemini review

[gemini-code-assist]

Code Review

This pull request implements logic to trigger Remote Config Realtime updates when experiment or variant assignments change. It introduces methods to load experiment payloads from the database, map them to configuration keys, and identify keys affected by changes in experiment metadata. Unit tests were added to verify these changes. Feedback suggests adding type safety checks when parsing experiment JSON to prevent crashes, using unionSet: for more concise set merging, and correcting an encoding constant in the test suite.