Checklist

• If applicable, unit tests
• If applicable, create follow-up issues for purchases-android and hybrids

Motivation

This change tightens the AdMob reward-verification API contract so integrations handle the resolved verification outcome by default, not only verification start. It improves correctness, aligns with stricter cross-platform direction, and matches AdMob rewarded-ad semantics where presentation requires a reward handler (OnUserEarnedRewardListener on Android / userDidEarnRewardHandler on iOS).

Description

Why

• Enforce that reward-verification flows consume the final resolved outcome.
• Keep flexibility for callers who intentionally ignore results ({ _ in }).
• Align adapter API with underlying platform-level rewarded-ad contracts.

What changed

• Breaking API update in RewardedAds+RewardVerification:
  • rewardVerificationStarted remains optional.
  • rewardVerificationResult is now required (non-optional, no default) for:
    • GoogleMobileAds.RewardedAd.present(...) (with and without placement)
    • GoogleMobileAds.RewardedInterstitialAd.present(...) (with and without placement)
• Internal handler update:
  • createUserDidEarnRewardHandler(...) now requires rewardVerificationResult.
  • Removed the optional callback guard path.
  • Kept missing-state behavior (warn + assert and .failed) and existing dispatch semantics.
• Tests:
  • Updated APISurfaceTests to reflect required callback signatures.
  • Removed nil callback usage from PresentRewardVerificationTests.
  • Preserved coverage for verified/failed outcomes, started-before-result ordering, and optional rewardVerificationStarted.

Migration impact

Before:

rewardedAd?.present(from: viewController)

After:

rewardedAd?.present(
    from: viewController,
    rewardVerificationResult: { result in
        // handle verified/failed result, or intentionally ignore with { _ in }
    }
)