chore(config-cat): Update ConfigCat providers to use the new ConfigCat SDK

[adams85]

This PR

Updates ConfigCat providers to use the new, unified ConfigCat SDK for JavaScript.

Also, improves the evaluation context to user object mapping to match the behavior of other ConfigCat OpenFeature providers. This comes with some minor breaking changes though:

• The targetingKey property is also included in the custom user attributes.
• If targetingKey is not specified, a User Object is still created and the identifier attribute is used as a fallback. In case that's not specified either, the SDK will use an empty string as the user identifier during feature flag evaluation.

Follow-up Tasks

The PR introduces significant breaking changes, so it should be released with an increased major version.

[gemini-code-assist]

Summary of Changes

Hello @adams85, 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 focuses on a significant upgrade of the ConfigCat OpenFeature providers by integrating the new, unified ConfigCat SDK. This modernization effort streamlines the underlying SDK usage and refines how user context is translated for feature flag evaluations, ensuring consistency and robustness across the providers. The changes also improve the readiness signal for the providers, making their state more transparent.

Highlights

• SDK Migration: The ConfigCat providers have been updated to use the new, unified ConfigCat SDK for JavaScript, replacing the separate configcat-js-ssr and configcat-node packages. This simplifies dependency management and aligns with the latest SDK architecture.
• Improved Evaluation Context Mapping: The mapping of evaluation context to ConfigCat user objects has been enhanced to match the behavior of other ConfigCat OpenFeature providers. This includes: 1. The targetingKey property is now explicitly included in the custom user attributes. 2. If targetingKey is not specified, the identifier attribute is used as a fallback for the user identifier. If neither is present, the SDK will use an empty string.
• Updated Error Handling and Event Emission: The providers now leverage the new EvaluationErrorCode from the unified SDK for more precise error translation, replacing the previous string-based error parsing. Additionally, the PROVIDER_READY event is now emitted more reliably based on the ConfigCat client's initialization state via its configChanged hook.

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[gemini-code-assist]

Code Review

This pull request is a significant and well-executed update, migrating the ConfigCat providers to the new unified ConfigCat SDK. The changes bring several improvements, including more robust error handling using error codes instead of string parsing, and a much cleaner provider readiness logic. The evaluation context mapping has been updated to align with other ConfigCat providers, which is a welcome standardization, although it introduces some breaking changes as noted in the description.

I've identified a high-severity issue regarding type safety when handling the identifier in the evaluation context, and a couple of medium-severity documentation inconsistencies that should be addressed to avoid confusion for developers using these providers.