feat: Use SyncContext from SyncFlagsResponse instead of Metadata Request

[marcozabel]

This PR

• This PR integrates the SyncContext from the SyncFlagsResponse into the Evaluation Context using the SyncMetadataHook.

Related Issues

Fixes #1350

[aepfli]

we do have e2e test for testing the sync context with gherkin, you can also enable those, to see if it is running properly :) https://github.com/open-feature/flagd-testbed/blob/1759a9491388e6c9714d5c048916120f77c8d892/gherkin/sync-payload.feature#L4 - those tests should normally work, if you add the missing provider configuration.

[toddbaert]

You're on the right track, but I think you need to add the transformation function I mentioned here.

[toddbaert]

Looks great! You only have one small issue, but it's one that will break things so I'm blocking for now: https://github.com/open-feature/js-sdk-contrib/pull/1401/files#r2546237260

[toddbaert]

/gemini review

[gemini-code-assist]

Code Review

This pull request integrates the SyncContext from the SyncFlagsResponse into the evaluation context, which is a valuable feature. The implementation introduces a new SyncMetadataHook and a contextEnricher configuration option. The overall approach is sound, but I've identified a critical issue with function binding that would lead to runtime errors, a couple of high-severity issues related to type safety and null handling, and a medium-severity suggestion to improve code clarity. Addressing these points will enhance the robustness of this new feature.

[aepfli]

we do have an e2e test within the test-bed for this. it seems like the submodule for the testbed in libs/shared/flagd-core is still pointing to an older version which does not contain those tests. can you please update the submodule to at least version https://github.com/open-feature/flagd-testbed/releases/tag/v2.11.0 - where those tests are added to verify this changes are correct. (a newer version would be even better but not needed)