ReviewPromptTrigger class

Wraps child and calls maybeRequestReview every time winStreakEvents fires (ENH-87) — the ready-to-use widget counterpart to in_app_review_helper.dart's decision logic, which the rest of the kit had no widget consuming at all before this. Same "core service has timing logic → widget listener wired to it" pattern as AchievementUnlockListener/AchievementService.

winStreakEvents is entirely caller-supplied — this widget doesn't invent its own "happy moment" source (there's no single game-agnostic event for that in this kit, unlike AchievementService.onUnlock). A consumer app fires an event on it with the player's CURRENT win streak count whenever a moment worth asking after happens (e.g. right after a level win), and maybeRequestReview's own minWinStreak/cooldown policy decides whether that particular event actually triggers a prompt.

everDeclined is read fresh from State.widget on every event (not cached at listen time), so a caller can flip it via setState on a parent and have the very next event respect the new value.

A showReview that throws (or a missing StorageService registration) is swallowed — same "never throws" defensive convention as AchievementUnlockListener — since a review-prompt failure must never crash the gameplay moment that triggered it.