FramebufferUIView: disable CALayer implicit animations on frame updates

Every time Mac repainted a region we set imageLayer.contents to a new
CGImage. CALayer's default action for .contents is a 0.25s crossfade, so
big repaints (like after a click — cursor + button + window-focus) looked
like a pulse. Tap seemed "flickery"; actually the whole view was doing
quarter-second crossfades constantly, most just weren't big enough to
notice until a chunky repaint hit.

Override imageLayer.actions with NSNull for contents/contentsRect/frame/
transform so blits are instantaneous, and wrap apply() in a
CATransaction.setDisableActions(true) for safety.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Packages/VNCUI/Sources/VNCUI/Session/FramebufferUIView.swift

@@ -86,6 +86,17 @@ final class FramebufferUIView: UIView,
         imageLayer.magnificationFilter = .nearest
         imageLayer.minificationFilter = .linear
         imageLayer.contentsGravity = .resize
+        // Kill CALayer's implicit animations — we want every framebuffer
+        // update to be an instantaneous blit, not a 0.25s crossfade.
+        imageLayer.actions = [
+            "contents": NSNull(),
+            "contentsRect": NSNull(),
+            "position": NSNull(),
+            "bounds": NSNull(),
+            "frame": NSNull(),
+            "transform": NSNull(),
+            "backgroundColor": NSNull()
+        ]
         layer.addSublayer(imageLayer)
 
         configureGestureRecognizers()
@@ -161,8 +172,11 @@ final class FramebufferUIView: UIView,
     }
 
     func apply(image: CGImage?, framebufferSize: CGSize) {
+        CATransaction.begin()
+        CATransaction.setDisableActions(true)
         imageLayer.contents = image
         applyLayerFrame()
+        CATransaction.commit()
     }
 
     private func applyLayerFrame() {