feat(admob): demonstrate rewarded interstitial ads

[polmiro]

Summary

Completes the Google Mobile Ads Next-Gen example app with rewarded-interstitial support and regression coverage:

• add direct and preloaded rewarded-interstitial workflows
• demonstrate optional RevenueCat reward verification
• add focused regression coverage for placement override callback handling

Screenshots

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Note

Low Risk
Changes are limited to the example app, documentation, and unit tests; no production adapter behavior is modified in this diff.

Overview
Finishes the AdMob Next-Gen sample app by replacing the rewarded-interstitial placeholder with a real screen and documenting how to run and validate every format.

Rewarded UI is refactored into a shared generic RewardedAdScreen used by both Rewarded and Rewarded interstitial. Each wires RevenueCat direct load, preload/poll, and show with format-specific placements, plus an optional RevenueCat reward verification toggle (applied at load/poll time).

Docs cross-link the sample and adapter READMEs and add guidance on direct vs preloaded flows, dashboard event checks, native test inventory caveats, and main-thread handling for SDK callbacks.

Tests: new PlacementOverrideTest covers applyPlacementOverride on tracking callbacks (update, clear, ignore non-tracking wrappers).

^{Reviewed by Cursor Bugbot for commit 44b412b. Bugbot is set up for automated code reviews on this repo. Configure here.}

[emerge-tools]

📸 Snapshot Test

621 unchanged

Name	Added	Removed	Modified	Renamed	Unchanged	Errored	Approval
TestPurchasesUIAndroidCompatibility com.revenuecat.testpurchasesuiandroidcompatibility	0	0	0	0	339	0	N/A
TestPurchasesUIAndroidCompatibility Paparazzi com.revenuecat.testpurchasesuiandroidcompatibility.paparazzi	0	0	0	0	282	0	N/A

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.19%. Comparing base (d3604f1) to head (44b412b).

Additional details and impacted files

@@                       Coverage Diff                       @@
##           next-gen-admob-sample-rewarded    #4045   +/-   ##
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  Coverage                           83.19%   83.19%           
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  Files                                 448      448           
  Lines                               18098    18098           
  Branches                             2736     2736           
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  Hits                                15057    15057           
  Misses                               2147     2147           
  Partials                              894      894           

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