Summary

Implements #120 (init timeout) and #121 (verify sync init succeeded) — the first step of the 1.0-readiness workstream A.

• A1 — initTimeout (default 30s) on both build and buildAsync private helpers.
  • Sync path: setProviderAndWait is wrapped with .disconnect.timeoutFail(TimeoutException(...))(initTimeout). The layer build fails fast instead of hanging on an unreachable / misconfigured provider.
  • Async path: a watchdog fiber forked into the layer's Scope sleeps initTimeout, then atomically transitions ProviderStatus.NotReady/Error to Fatal so callers polling providerStatus stop waiting. The fiber is interrupted when the layer is released.
  • Public overloads fromProvider(provider, evaluationTimeout, initTimeout) and fromProviderAsync(provider, evaluationTimeout, initTimeout) added for explicit control. All existing factories inherit the 30s default — no caller code needs to change.
• A2 — Verify sync init. After setProviderAndWait returns, the new verifyInitState helper reads the underlying provider's state. READY / STALE are accepted; ERROR / FATAL / NOT_READY cause the layer build to fail with an IllegalStateException so misconfiguration surfaces at startup instead of at first evaluation.

New cases in core/src/test/scala/zio/openfeature/ProviderInitHardeningSpec.scala:

• Sync fromProvider fails with TimeoutException when init blocks past initTimeout.
• Sync fromProvider fails with IllegalStateException when provider reports ERROR after initialize().
• Async watchdog transitions ProviderStatus to Fatal after initTimeout when init hangs.

Closes #120
Closes #121