[#471] CompactBlockValidationOperation to async (#515)

- CompactBlockValidationOperation wrapped to Task

Sources/ZcashLightClientKit/Block/Processor/CompactBlockValidationInformation.swift

@@ -22,6 +22,8 @@ class CompactBlockValidationOperation: ZcashOperation {
     private var cacheDb: URL
     private var dataDb: URL
     private var network: NetworkType
+    private var cancelableTask: Task<Void, Error>?
+    private var done = false
 
     init(
         rustWelding: ZcashRustBackendWelding.Type,
@@ -44,6 +46,7 @@ class CompactBlockValidationOperation: ZcashOperation {
 
         self.startedHandler?()
 
+        cancelableTask = Task {
             let result = self.rustBackend.validateCombinedChain(dbCache: cacheDb, dbData: dataDb, networkType: self.network)
             
             switch result {
@@ -54,6 +57,7 @@ class CompactBlockValidationOperation: ZcashOperation {
                 self.fail(error: error)
                 
             case ZcashRustBackendWeldingConstants.validChain:
+                self.done = true
                 break
                 
             default:
@@ -63,4 +67,19 @@ class CompactBlockValidationOperation: ZcashOperation {
                 self.fail(error: error)
             }
         }
+        
+        while !done && !isCancelled {
+            sleep(1)
+        }
+    }
+    
+    override func fail(error: Error? = nil) {
+        self.cancelableTask?.cancel()
+        super.fail(error: error)
+    }
+    
+    override func cancel() {
+        self.cancelableTask?.cancel()
+        super.cancel()
+    }
 }