fix: QR scanner crash - add previewLayer as sublayer in layout() instead of init

Sources/QRScannerView.swift

@@ -91,7 +91,7 @@ class QRScannerHostView: NSView {
     override init(frame: CGRect) {
         super.init(frame: frame)
         wantsLayer = true
-        layer = previewLayer
+        // 不在 init 时设置 layer = previewLayer，等 layout 时再添加为 sublayer
     }
     
     required init?(coder: NSCoder) {
@@ -100,6 +100,9 @@ class QRScannerHostView: NSView {
     
     override func layout() {
         super.layout()
+        if previewLayer.superlayer == nil {
+            layer?.addSublayer(previewLayer)
+        }
         previewLayer.frame = bounds
     }
 }