feat(android): add foss flavor build without gms services (#3666)

apps/readest-app/src-tauri/plugins/tauri-plugin-native-bridge/android/src/foss/java/com/readest/native_bridge/BillingManager.kt

@@ -0,0 +1,31 @@
+package com.readest.native_bridge
+
+import android.app.Activity
+import android.util.Log
+
+class BillingManager(private val activity: Activity) {
+    companion object {
+        private const val TAG = "BillingManager"
+    }
+
+    fun isBillingAvailable(): Boolean {
+        return false
+    }
+
+    fun initialize(callback: (Boolean) -> Unit) {
+        Log.d(TAG, "Google Play billing not available in this build")
+        callback(false)
+    }
+
+    fun fetchProducts(productIds: List<String>, callback: (List<ProductData>) -> Unit) {
+        callback(emptyList())
+    }
+
+    fun purchaseProduct(productId: String, callback: (PurchaseData?) -> Unit) {
+        callback(null)
+    }
+
+    fun restorePurchases(callback: (List<PurchaseData>) -> Unit) {
+        callback(emptyList())
+    }
+}