Centralize type dispatch in ClientEvaluator, fix addApiHook singleton bypass, simplify TestFeatureProvider Hub

[EtaCassiopeia]

Summary

ClientEvaluator: centralized type dispatch replaces repetitive string-match arms

evaluateFromClient had 6 identical case "Type" => evaluateViaTypeclass(key, default.asInstanceOf[Type], ...) arms. Added ClientEvaluator.evaluateStandard that centralizes the type-name → evaluator lookup, reducing the match to a single case Some(...) arm. Object and custom type paths remain as special cases.

addApiHook / clearApiHooks bypass isolated OpenFeatureAPI instances

These were static companion methods calling OpenFeatureAPI.getInstance() — the global singleton. When FeatureFlagRegistry creates clients with isolated API instances via OpenFeatureAPIFactory.create(), hooks added through the companion never reached those clients. Moved to FeatureFlags trait methods, implemented in FeatureFlagsLive using the injected api instance. Companion accessors now delegate through the service.

TestFeatureProvider: Ref[Hub] replaced with plain Hub

eventsHubRef: Ref[Hub[ProviderEvent]] was never updated to a new Hub — the Ref added unnecessary indirection on every event publish and stream subscription. Replaced with a direct eventsHub: Hub[ProviderEvent] field.

Not addressed (cross-compilation constraints)

• implicit → given/using: required for Scala 2.13 compatibility in shared source
• CountDownLatch → ZIO Promise: Java SDK's initialize() requires actual thread blocking at the Java/ZIO boundary