Fix #1297: configurable rewarded completion timeout

[mdanylov-sigma]

Summary

Makes the previously hard-coded 120s RewardedConfig.defaultCompletionTime publisher-configurable via a new rewardedCompletionTimeout property on VideoControlsConfiguration (default 120, matching prior behavior), with pass-throughs on RewardedAdUnit, MediationBaseInterstitialAdUnit, and a new direct property on InterstitialController.

Closes #1297

Behavior

• Rejects negative values safely (logs a warning, keeps the previous value) rather than throwing or silently accepting bad state.
• Propagates through both DisplayView.loadAd() and InterstitialController.loadAd() into RewardedConfig.defaultCompletionTime before the transaction factory is created.
• Used only as a fallback for the endcard/banner rewarded-completion timer (PBMHTMLCreative.setupRewardTimerIfNeeded) when the bid omits endcardTime/bannerTime — it does not affect the primary VAST video reward-completion path (playback-event/percentage based), which is unrelated and untouched.

Testing

• PrebidMobileTests (unit): 22/22 passed, including new tests:
  • testRewardedCompletionTimeout (default/override/negative-rejection)
  • testInterstitialControllerPropagatesRewardedCompletionTimeout — exercises InterstitialController.loadAd() end-to-end and asserts rewardedConfig.defaultCompletionTime reflects the configured value.
  • testDisplayViewPropagatesRewardedCompletionTimeout — same for DisplayView.loadAd().
  • testRewardEvent_EndcardUsesConfiguredFallback

API / compatibility

• RewardedConfig.defaultCompletionTime changes let → var: additive, non-breaking for Objective-C consumers.
• New TimeInterval properties are plain @objcMembers-compatible, consistent with existing config surface.

[OlenaPostindustria]

Also, worth adding the new property to public docs

[OlenaPostindustria]

LGTM!

[YuriyVelichkoPI]

Blocked since there is a way to implement the requested functionality without changes in the SDK:
#1297 (comment)

[mdanylov-sigma]

The supported rwdd passthrough and setImpORTBConfig approach is now documented in prebid/prebid.github.io#6697. I have left this SDK PR open because the latest review rejects the SDK API itself, so closing or withdrawing it requires an explicit decision.