Add support for SwiftUI environment

Example/Example/ExampleApp.swift

@@ -1,10 +1,17 @@
 import SwiftUI
+import Perception
 
 @main
 struct ExampleApp: App {
+  let model = CounterModel()
+
   var body: some Scene {
-    WindowGroup {
-      ContentView(model: CounterModel())
+    WithPerceptionTracking {
+      let _ = print("!!!")
+//      let _ = model.count
+      WindowGroup {
+        ContentView(model: model)
+      }
     }
   }
 }

Sources/Perception/Environment.swift

@@ -0,0 +1,62 @@
+import SwiftUI
+
+extension Environment {
+  @available(iOS, introduced: 13, obsoleted: 17)
+  @available(macOS, introduced: 10.15, obsoleted: 14)
+  @available(tvOS, introduced: 13, obsoleted: 17)
+  @available(watchOS, introduced: 6, obsoleted: 10)
+  @available(visionOS, unavailable)
+  @_disfavoredOverload
+  public init(_ objectType: Value.Type) where Value: AnyObject & Perceptible {
+    self.init(\.[unwrap: \Value.self])
+  }
+
+  @available(iOS, introduced: 13, obsoleted: 17)
+  @available(macOS, introduced: 10.15, obsoleted: 14)
+  @available(tvOS, introduced: 13, obsoleted: 17)
+  @available(watchOS, introduced: 6, obsoleted: 10)
+  @available(visionOS, unavailable)
+  @_disfavoredOverload
+  public init<T: AnyObject & Perceptible>(_ objectType: T.Type) where Value == T? {
+    self.init(\.[\T.self])
+  }
+}
+
+extension View {
+  @available(iOS, introduced: 13, obsoleted: 17)
+  @available(macOS, introduced: 10.15, obsoleted: 14)
+  @available(tvOS, introduced: 13, obsoleted: 17)
+  @available(watchOS, introduced: 6, obsoleted: 10)
+  @available(visionOS, unavailable)
+  public func environment<T: AnyObject & Perceptible>(_ object: T?) -> some View {
+    self.environment(\.[\T.self], object)
+  }
+}
+
+private struct PerceptibleKey<T: Perceptible>: EnvironmentKey {
+  static var defaultValue: T? { nil }
+}
+
+extension EnvironmentValues {
+  fileprivate subscript<T: Perceptible>(_: KeyPath<T, T>) -> T? {
+    get { self[PerceptibleKey<T>.self] }
+    set { self[PerceptibleKey<T>.self] = newValue }
+  }
+}
+
+extension EnvironmentValues {
+  fileprivate subscript<T: Perceptible>(unwrap _: KeyPath<T, T>) -> T {
+    get {
+      guard let object = self[\T.self] else {
+        fatalError(
+          """
+          No perceptible object of type \(T.self) found. A View.environment(_:) for \(T.self) may \
+          be missing as an ancestor of this view.
+          """
+        )
+      }
+      return object
+    }
+    set { self[\T.self] = newValue }
+  }
+}