feat(ads): ad reward tracking with admob adapter (#3885)

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### Description

This change is the admob adapter wiring for ad reward tracking. AdMob
adapter automatically manages polling of the result and so we wire up
the tracking metadata automatically here.

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---

> [!NOTE]
> **Medium Risk**
> Touches reward verification and ad event correlation paths; behavior
change for poll parameters (metadata + ADAPTER) but scoped to AdMob
adapter wiring with test coverage.
> 
> **Overview**
> When a rewarded ad earns a reward through the AdMob adapter’s
verification flow, **reward verification polling** now includes **ad
tracking metadata** and marks capture as **adapter-driven**
(`AdCaptureMethod.ADAPTER`).
> 
> For ads loaded via `loadAndTrackRewardedAd` /
`loadAndTrackRewardedInterstitialAd`, metadata is read from the wrapped
`TrackingFullScreenContentCallback` (network, mediator, format, unit id,
impression id, and **placement at reward time**). Untracked ads still
poll with **null** metadata.
> 
> `TrackingFullScreenContentCallback` adds `rewardTrackingMetadata()` so
placement overrides applied before show are reflected in verification
tracking.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
da9cdd404221bb58f083f9b39776bb35ce96cee2. Bugbot is set up for automated
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