feat: merge rustore test UI and unify SKU format across channels

- Merge VK login/link/check and Review test buttons from dev_rustore
- Unify Rustore/GooglePlay SKU format via ChannelHelpers.normalizeSkuList()
- Fix ChannelConfig runtime sync: Java InitSDK sets channel from ChannelHelpers.CHANNEL
- Fix AndroidMinSdkVersion 25→26 for tuyoosdk compatibility
- Fix Flexion AndroidManifest tools:replace missing fullBackupContent value
- Add [CHANNEL-VERIFY] debug logs for channel verification

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ExtraPluginCfgs/Android/flexion/ChannelHelpers.java

@@ -1,9 +1,17 @@
 package com.unity3d.player;
 
 public class ChannelHelpers {
+    
     public static final String CHANNEL = "Flexion";
 
     static void register() {
         SDKManager.registerHelper(CHANNEL, new FlexionSDKHelper());
     }
+
+
+    // Flexion provides price in micros and currency code, so no normalization needed
+    // 支付的变化，可能会修改这里
+    public static String normalizeSkuList(String msg) {
+        return msg;
+    }
 }