Spec v0.9.0 compliance

Tracks [spec v0.9.0](https://github.com/open-feature/spec/releases/tag/v0.9.0) compliance. No events subsystem yet (blocks provider-state item).

- [ ] #93 Events subsystem
- [ ] #102 Hook data
- [ ] #96 Telemetry utility ([Appendix D](https://openfeature.dev/specification/appendix-d))
- [ ] #124 Provider `shutdown` on `api.shutdown()` ([spec 2.5.3](https://openfeature.dev/specification/sections/providers))
- [ ] #135 Domain in provider init
- [ ] Tracking ([spec 6](https://openfeature.dev/specification/sections/tracking))
- [ ] Isolated API instances (bless + document)
- [ ] Multi-provider (optional)

- [ ] Provider lifecycle event ownership (race-condition fix): add opt-in marker so providers emit their own `PROVIDER_READY`/`PROVIDER_ERROR`; SDK derives status from the provider event stream and keeps + deprecates the legacy synthetic path; update first-party providers ([spec 5.3.5](https://openfeature.dev/specification/sections/events#requirement-535), [provider status 2.8](https://openfeature.dev/specification/sections/providers#28-provider-status), [Appendix E](https://openfeature.dev/specification/appendix-e))

Start by reviewing the linked Spec v0.9.0 release and the referenced issues (#93, #102, #96, #124, and #135), then inspect the specification sections cited in the checklist. Done means the listed compliance items, tracking work, isolated API documentation, optional multi-provider support, and provider lifecycle event ownership are resolved and the checklist can be verified.

Written by the indexing model from the issue text.