video_player + insets: native playback backend + animated viewPadding

- video_player: ExoPlayer (Android) / AVPlayer (iOS/macOS) backend with
  PixelBufferSink, method-channel adapter, Dart-side XVideoPlayer +
  testing fake.
- insets: XInsets singleton + XAnimatedInsets widget lerp the system
  viewPadding over 220ms so OS bar visibility toggles
  (immersiveSticky <-> edgeToEdge) slide bottom-/top-anchored UI into
  place instead of snapping by the nav-bar / status-bar height.

macos/Classes/Video-shared/VideoPlayerPlugin.swift

@@ -0,0 +1,205 @@
+import AVFoundation
+import Foundation
+#if canImport(UIKit)
+import Flutter
+#else
+import FlutterMacOS
+#endif
+
+/// `ux/video` + `ux/video/events` registrar. Routes channel calls to
+/// per-handle [UxVideoPlayerInstance]s. Mirrors `CameraPlugin`'s shape.
+public class UxVideoPlayerPlugin: NSObject, NativePlugin, FlutterStreamHandler {
+    private weak var textureRegistry: FlutterTextureRegistry?
+    private var instances: [Int: UxVideoPlayerInstance] = [:]
+    private var nextHandle: Int = 1
+    private var eventSink: FlutterEventSink?
+
+    public func register(with registrar: FlutterPluginRegistrar) {
+        textureRegistry = registrar.uxTextures
+
+        let methods = FlutterMethodChannel(
+            name: "ux/video",
+            binaryMessenger: registrar.uxMessenger,
+        )
+        methods.setMethodCallHandler { [weak self] call, result in
+            self?.handle(call, result: result)
+        }
+
+        let events = FlutterEventChannel(
+            name: "ux/video/events",
+            binaryMessenger: registrar.uxMessenger,
+        )
+        events.setStreamHandler(self)
+    }
+
+    // MARK: - FlutterStreamHandler
+
+    public func onListen(
+        withArguments arguments: Any?,
+        eventSink events: @escaping FlutterEventSink,
+    ) -> FlutterError? {
+        eventSink = events
+        return nil
+    }
+
+    public func onCancel(withArguments arguments: Any?) -> FlutterError? {
+        eventSink = nil
+        return nil
+    }
+
+    // MARK: - Dispatch
+
+    private func handle(_ call: FlutterMethodCall, result: @escaping FlutterResult) {
+        switch call.method {
+        case "create":
+            create(args: call.arguments, result: result)
+        case "initialize":
+            withInstance(call.arguments, result: result) { instance in
+                instance.prepare { error, size, durationMs, rotationQuarterTurns in
+                    DispatchQueue.main.async {
+                        if let error = error {
+                            result(
+                                FlutterError(
+                                    code: "decode_failed",
+                                    message: error.localizedDescription,
+                                    details: nil,
+                                )
+                            )
+                            return
+                        }
+                        result(
+                            [
+                                "size": [
+                                    "width": Double(size.width),
+                                    "height": Double(size.height),
+                                ] as [String: Any],
+                                "durationMs": durationMs,
+                                "rotationQuarterTurns": rotationQuarterTurns,
+                            ] as [String: Any]
+                        )
+                    }
+                }
+            }
+        case "dispose":
+            withInstance(call.arguments, result: result) { instance in
+                self.instances.removeValue(forKey: instance.handle)
+                instance.dispose()
+                result(nil)
+            }
+        case "play":
+            withInstance(call.arguments, result: result) { instance in
+                instance.play()
+                result(nil)
+            }
+        case "pause":
+            withInstance(call.arguments, result: result) { instance in
+                instance.pause()
+                result(nil)
+            }
+        case "seekTo":
+            guard let args = call.arguments as? [String: Any],
+                  let pos = (args["positionMs"] as? NSNumber)?.int64Value
+            else {
+                result(badArgs("seekTo"))
+                return
+            }
+            withInstance(args, result: result) { instance in
+                instance.seekTo(positionMs: pos)
+                result(nil)
+            }
+        case "setLooping":
+            guard let args = call.arguments as? [String: Any],
+                  let loop = args["loop"] as? Bool
+            else {
+                result(badArgs("setLooping"))
+                return
+            }
+            withInstance(args, result: result) { instance in
+                instance.setLooping(loop)
+                result(nil)
+            }
+        case "setVolume":
+            guard let args = call.arguments as? [String: Any],
+                  let volume = (args["volume"] as? NSNumber)?.floatValue
+            else {
+                result(badArgs("setVolume"))
+                return
+            }
+            withInstance(args, result: result) { instance in
+                instance.setVolume(volume)
+                result(nil)
+            }
+        case "setPlaybackSpeed":
+            guard let args = call.arguments as? [String: Any],
+                  let rate = (args["rate"] as? NSNumber)?.floatValue
+            else {
+                result(badArgs("setPlaybackSpeed"))
+                return
+            }
+            withInstance(args, result: result) { instance in
+                instance.setPlaybackSpeed(rate)
+                result(nil)
+            }
+        default:
+            result(FlutterMethodNotImplemented)
+        }
+    }
+
+    private func create(args: Any?, result: @escaping FlutterResult) {
+        guard let dict = args as? [String: Any],
+              let uri = dict["uri"] as? String,
+              let registry = textureRegistry
+        else {
+            result(badArgs("create"))
+            return
+        }
+        guard let url = URL(string: uri) else {
+            result(badArgs("create uri"))
+            return
+        }
+        let handle = nextHandle
+        nextHandle += 1
+        let instance = UxVideoPlayerInstance(handle: handle, registry: registry)
+        instance.onEvent = { [weak self] payload in
+            DispatchQueue.main.async {
+                self?.eventSink?(payload)
+            }
+        }
+        instance.setSource(url: url)
+        instances[handle] = instance
+        result(
+            [
+                "handle": handle,
+                "textureId": instance.textureId,
+            ] as [String: Any]
+        )
+    }
+
+    private func withInstance(
+        _ args: Any?,
+        result: @escaping FlutterResult,
+        body: (UxVideoPlayerInstance) -> Void,
+    ) {
+        guard let dict = args as? [String: Any],
+              let handle = (dict["handle"] as? NSNumber)?.intValue
+        else {
+            result(badArgs("missing handle"))
+            return
+        }
+        guard let instance = instances[handle] else {
+            result(
+                FlutterError(
+                    code: "disposed",
+                    message: "no player for handle \(handle)",
+                    details: nil,
+                )
+            )
+            return
+        }
+        body(instance)
+    }
+
+    private func badArgs(_ method: String) -> FlutterError {
+        FlutterError(code: "bad_args", message: method, details: nil)
+    }
+}