[#470] CompactBlockStreamDownloadOperation to async (#506)

- using new sync APIs for storage and service
- whole logic wrapped in the Task

Closes #470

Sources/ZcashLightClientKit/Block/Processor/CompactBlockDownloadOperation.swift

@@ -71,7 +71,6 @@ class CompactBlockStreamDownloadOperation: ZcashOperation {
     private var storage: CompactBlockStorage
     private var service: LightWalletService
     private var done = false
-    private var cancelable: CancellableCall?
     private var cancelableTask: Task<Void, Error>?
     private var startHeight: BlockHeight?
     private var targetHeight: BlockHeight?
@@ -120,14 +119,15 @@ class CompactBlockStreamDownloadOperation: ZcashOperation {
         }
         self.startedHandler?()
         
+        cancelableTask = Task {
             do {
                 if self.targetHeight == nil {
-                self.targetHeight = try service.latestBlockHeight()
+                    self.targetHeight = try await service.latestBlockHeightAsync()
                 }
                 guard let latestHeight = self.targetHeight else {
                     throw LightWalletServiceError.generalError(message: "missing target height on block stream operation")
                 }
-            let latestDownloaded = try storage.latestHeight()
+                let latestDownloaded = try await storage.latestHeightAsync()
                 let startHeight = max(self.startHeight ?? BlockHeight.empty(), latestDownloaded)
                 
                 let stream = service.blockStream(
@@ -135,8 +135,6 @@ class CompactBlockStreamDownloadOperation: ZcashOperation {
                     endHeight: latestHeight
                 )
                 
-            cancelableTask = Task {
-                do {
                 for try await zcashCompactBlock in stream {
                     try self.cache(zcashCompactBlock, flushCache: false)
                     let progress = BlockProgress(
@@ -160,19 +158,14 @@ class CompactBlockStreamDownloadOperation: ZcashOperation {
         while !done && !isCancelled {
             sleep(1)
         }
-        } catch {
-            self.fail(error: error)
-        }
     }
 
     override func fail(error: Error? = nil) {
-        self.cancelable?.cancel()
         self.cancelableTask?.cancel()
         super.fail(error: error)
     }
     
     override func cancel() {
-        self.cancelable?.cancel()
         self.cancelableTask?.cancel()
         super.cancel()
     }