fix: reprepare reward ad after dismissal (#16)

Reward units never set intervals[], so the shared reprepare(adObject:)
guard was returning early and never reloading the ad. Move the interval
guard inside the interstitial/opening branches only, so reward ads
always reload after dismissal.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: 2sem

GADManager/GADManager.swift

@@ -362,15 +362,17 @@ public class GADManager<E : RawRepresentable> : NSObject, GoogleMobileAds.FullSc
     }
 
     func reprepare(adObject: NSObject, isTesting: Bool = false){
-        guard let name = self.name(forAdObject: adObject), let unit = E.init(rawValue: name), let interval = self.intervals[unit] else{
+        guard let name = self.name(forAdObject: adObject), let unit = E.init(rawValue: name) else{
             return;
         }
-        
+
         let isTesting = self.isTesting[unit] ?? isTesting;
 
         if adObject is GoogleMobileAds.InterstitialAd{
+            guard self.intervals[unit] != nil else { return }
             self.reprepare(interstitialUnit: unit, isTesting: isTesting);
         }else if adObject is GoogleMobileAds.AppOpenAd{
+            guard self.intervals[unit] != nil else { return }
             self.reprepare(openingUnit: unit, isTesting: isTesting);
         }else if adObject is GoogleMobileAds.RewardedAd{
             self.reprepare(rewardUnit: unit, isTesting: isTesting);