chore: call refreshHandler once and even if features are up to date

[nekrich]

Summary

This PR makes refreshHandler behave as a single completion signal. It is now called once for network success/failure handling and for the case where cached features are still fresh and no network request is needed.
This allows us to determine the sate of the GrowthBookSDK and if the features are ready or not.

Problem

refreshCache() delegates to FeaturesViewModel.fetchFeatures, but the previous callback flow only notified refreshHandler from specific success or failure delegate paths and could call it several times. That meant a refresh could restore cached features and finish without notifying callers, so consumers could not reliably treat refreshHandler as a "ready" signal.

Remote evaluation also had two issues in the previous flow:

• When remoteEval was enabled and the cache was expired, fetchFeatures started both the regular feature fetch and the remote-evaluation fetch.
• The cache-expiration check only guarded the regular feature fetch; the remote-evaluation fetch still ran even when cached data was fresh.

There was also a duplicate-notification risk because both featuresFetchedSuccessfully and savedGroupsFetchedSuccessfully could call refreshHandler during the same response handling path.

Solution

The change introduces a single delegate method, featuresUpdateIsComplete(error:isRemote:), and routes refreshHandler through that method instead of calling it from individual feature and saved-group success/failure callbacks.

FeaturesViewModel.fetchFeatures now:

• Reports .invalidAPIURL when no API URL is available.
• Reports completion with no error when cached features are up to date.
• Uses the cache-expiration check before choosing either the remote-evaluation fetch or the regular feature fetch.
• Calls the completion delegate once after remote fetch handling succeeds or fails.

GrowthBookSDK keeps featuresFetchFailed and savedGroupsFetchFailed as no-op delegate methods, if you want me to delete them just ask 😅.

Tests

The patch adds regression coverage for:

• refreshHandler firing when refreshCache() is called while features are already cached.
• featuresUpdateIsComplete being called once for remote-evaluation success and failure.
• featuresUpdateIsComplete being called when cached features are fresh.

[vazarkevych]

Hi @nekrich,
thanks for your contribution. The work looks good and the fix is more efficient. Please take a look at the comments - once addressed, I'll happily approve and merge. 🙌

[vazarkevych]

erorr typo - also appears on lines 95 and 101.

[nekrich]

Fixed in c25abd8

[vazarkevych]

isRemote guard is not needed here. I believe we can remove this parameter.

[nekrich]

Fixed in 0605a13

[vazarkevych]

With isRemote: false it won't fire refreshHandler.

[nekrich]

Good catch. Fix is in 0605a13