Fix Swift 6.1 strict concurrency errors in timer/callback bridging

Task closures that captured self from non-isolated callbacks
(Timer.scheduledTimer, VTCompressionSession output, SCStream output)
were failing on Swift 6.1 with "reference to captured var 'self' in
concurrently-executing code". Explicitly recapture with [weak self] at
the Task boundary.

FrameOutputStream also needed an UncheckedSendableBox wrapper to pass
CMSampleBuffer (non-Sendable) from the compression callback into a
MainActor Task without a sending warning.

Verified with swift build locally; Swift 6.3 was lenient about the
original patterns but Swift 6.1 on the CI runner was not.

Author: xocialize

Sources/VirtualDisplayKit/Core/DisplayRecorder.swift

@@ -288,7 +288,7 @@ public final class DisplayRecorder: ObservableObject {
 
         // Start duration timer
         durationTimer = Timer.scheduledTimer(withTimeInterval: 0.1, repeats: true) { [weak self] _ in
-            Task { @MainActor in
+            Task { @MainActor [weak self] in
                 self?.updateDuration()
             }
         }

Sources/VirtualDisplayKit/Core/DisplayStreamRenderer.swift

@@ -205,7 +205,7 @@ public final class DisplayStreamRenderer: NSView {
 
                 // Create output handler
                 let output = SCStreamOutputHandler { [weak self] surface, pixelBuffer in
-                    Task { @MainActor in
+                    Task { @MainActor [weak self] in
                         self?.handleFrame(surface: surface, pixelBuffer: pixelBuffer)
                     }
                 }

Sources/VirtualDisplayKit/Core/FrameOutputStream.swift

@@ -12,6 +12,13 @@ import CoreMedia
 import CoreVideo
 import VideoToolbox
 
+// Wrapper to cross Sendable boundaries for Core Media types that are not
+// themselves Sendable but are safe to hand off to MainActor work.
+private struct UncheckedSendableBox<Value>: @unchecked Sendable {
+    let value: Value
+    init(_ value: Value) { self.value = value }
+}
+
 /// Delegate for receiving streaming frames
 @MainActor
 public protocol FrameOutputStreamDelegate: AnyObject {
@@ -365,10 +372,10 @@ public final class FrameOutputStream: ObservableObject {
             frameProperties: nil,
             infoFlagsOut: &flags
         ) { [weak self] status, infoFlags, sampleBuffer in
-            guard let self = self, status == noErr, let buffer = sampleBuffer else { return }
-            
-            Task { @MainActor in
-                self.handleEncodedFrame(buffer)
+            guard status == noErr, let buffer = sampleBuffer else { return }
+            let sendableBuffer = UncheckedSendableBox(buffer)
+            Task { @MainActor [weak self] in
+                self?.handleEncodedFrame(sendableBuffer.value)
             }
         }