Report THEOads interstitial errors as failed ads to Conviva

[tvanlaerhoven]

Problem
A THEOads (SGAI) ad break can fail before any ad exists - e.g. an empty VAST response makes the ad request fail before an ad break is created. In that case no adbreakbegin/adbegin/aderror is dispatched, only THEOads' interstitialerror, which the Conviva connector didn't listen to. Conviva therefore never saw an ad attempt, and fill rate looked like 100%.

Solution
The connector now listens to interstitialerror on the THEOads integration. For ad break interstitials that fail while no ad break is active, it reports:

reportAdBreakStarted → setAdInfo → reportAdFailed(message) → reportAdBreakEnded

Errors during an ongoing break keep using the existing aderror path, so nothing is reported twice.

Implementation notes

• Ad break info comes from a calculateInterstitialAdBreakInfo() helper that reports POD_POSITION (derived from the interstitial start time: pre-roll at 0, post-roll at negative/infinite, else mid-roll), POD_DURATION and POD_INDEX. The pod index shares the same sequential counter as regular ad breaks.
• Ad metadata shared between the successful and failed ad paths (c3.csid, contentAssetName) is collected by a single collectBaseAdMetadata() helper.
• The ad technology is reported as "Server Guided" via one shared constant (SGAI isn't officially supported by Conviva yet). reportAdBreakStarted itself reports SERVER_SIDE on Android/iOS where the parameter is enum-typed.
• Shipped as a new THEOplayer-Connector-Conviva/THEOads CocoaPods subspec; SPM builds compile the code out via canImport since the THEOads integration isn't an SPM dependency.