feat: upgrade OpenFeature SDK to 0.8.0

[nicklasl]

Summary

• Upgrade OpenFeature Kotlin SDK from 0.6.2 to 0.8.0.
• Implement the 0.8 provider lifecycle event flow for initialize/onContextSet, including ready, error, and stale states.
• Add result-returning suspend context APIs (putContextAndWait, removeContextAndWait) for Provider reconciliation.

Testing

• ./gradlew :Confidence:testDebugUnitTest --tests com.spotify.confidence.ActivateAndFetchAsyncRaceConditionTest :Provider:testDebugUnitTest --tests com.spotify.confidence.openfeature.ConfidenceFeatureProviderTrackTest :Confidence:apiCheck :Provider:apiCheck --offline
• ./gradlew :Confidence:ktlintCheck :Provider:ktlintCheck --offline
• git diff --check

Compatibility

• OpenFeature remains exposed via api(...), so downstream consumers that directly use OpenFeature Kotlin SDK types will see 0.8.0 and may need to adapt to the 0.7/0.8 provider lifecycle API.
• Existing Confidence context APIs remain available; this adds putContextAndWait and collection-based removeContextAndWait instead of exposing a Provider-specific reconciliation method.
• Full Provider unit test run still has the pre-existing remote fixture failures in ProviderIntegrationTest for kotlin-test-flag.my-integer, reproduced on clean HEAD before this change.