refactor(admob): reuse suspended load tracking for interstitial ads

[polmiro]

Summary

I jumped the gun and merged the approved PR for interstitial ads before adopting the new helper.

• refactor(admob): share suspended ad load result tracking #4053 introduced the shared AdLoadResult.trackAndConfigureAdLoadResult foundation helper.
• Adopt that helper at the existing suspending interstitial load call site while preserving result identity, tracking order, and callback installation.

Test plan

• ./gradlew :feature:admob-next-gen:testDefaultsDebugUnitTest
• ./gradlew detektAll
• ./scripts/api-check.sh

---

Note

Low Risk
Mechanical refactor to a shared helper with equivalent tracking and callback wiring; no API or auth changes.

Overview
The suspending AdTracker.loadAndTrackInterstitialAd path no longer inlines success/failure tracking with trackAdLoaded / trackAdFailedToLoad. It now chains InterstitialAd.load through the shared trackAndConfigureAdLoadResult helper (from #4053), passing interstitial format metadata and a configureAd block that installs the tracking event callback.

Behavior is intended to stay the same: the original AdLoadResult is returned, load success/failure events are still tracked, and tracking is installed on successful loads before the suspend function completes.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.99%. Comparing base (40b51c5) to head (9a4b7f0).
⚠️ Report is 1 commits behind head on next-gen-admob-sdk.

Additional details and impacted files

@@                  Coverage Diff                   @@
##           next-gen-admob-sdk    #4086      +/-   ##
======================================================
- Coverage               83.01%   82.99%   -0.02%     
======================================================
  Files                     437      437              
  Lines                   17893    17893              
  Branches                 2684     2684              
======================================================
- Hits                    14854    14851       -3     
- Misses                   2146     2148       +2     
- Partials                  893      894       +1     

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[polmiro]

Going ahead merging this one since it was an oversight and practically the same commit is being applied in every ad format branch.