feat(provider): add Statsig Remote Config provider

[kirich1409]

Goal

Implement RemoteConfigValueProvider backed by Statsig.

Rationale

Statsig is a popular SaaS feature-flag + experimentation platform; analytics-heavy teams expect support out of the box.

Scope

Statsig ships Kotlin and Swift SDKs (no KMP). Split into two providers:

• providers:statsig-android — wraps com.statsig:statsig-android (mirror providers/firebase/).
• providers:statsig-ios — wraps the Swift Statsig SDK via cinterop, exposed through a Kotlin facade (mirror providers/nsuserdefaults/ packaging).

Supported types: Boolean, String, Int, Long, Double, Float; enums by name.

References

• Interface: core/src/commonMain/kotlin/dev/androidbroadcast/featured/RemoteConfigValueProvider.kt
• Android-only reference: providers/firebase/
• iOS-only reference: providers/nsuserdefaults/

Definition of Done

• New module(s) under providers/ published to Maven Central
• Unit tests with mocked Statsig client
• Sample wiring
• Wiki Providers page updated
• CHANGELOG.md [Unreleased] entry
• ./gradlew spotlessCheck && ./gradlew check clean