✨ Add ToastItem, ToastView, ToastGroup, RootView, and Toast classes

Added ToastItem struct with custom properties and Timing enum for toast item
Added ToastView struct for displaying toast item with symbol image and title
Added ToastGroup struct for managing multiple toast views in a ZStack
Added RootView struct for setting up UIWindow for overlay window to display toast
Added Toast class with present method to add toast items to display on RootView

Shared/Sources/DesignSystem/Components/Toast/Toast.swift

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+//
+//  Toast.swift
+//
+//
+//  Created by 홍승현 on 3/24/24.
+//
+
+import SwiftUI
+
+@Observable
+public final class Toast {
+  /// Since the class conforms to the Observable protocol,
+  /// we can use this singleton object as a state object to receive UI updates on the overlay window root controller
+  public static let shared = Toast()
+  var toasts: [ToastItem] = []
+
+  /// 토스트를 띄웁니다.
+  /// - Parameters:
+  ///   - title: 토스트 제목
+  ///   - symbol: 토스트에 들어갈 `SF Symbol` 이미지 문자열 값
+  ///   - tint: 토스트의 틴트 색상
+  ///   - isUserInteractionEnabled: 사용자의 상호작용 여부, 스스로 지우거나 못하도록 설정할 수 있습니다.
+  ///   - duration: 토스트 유지 시간
+  public func present(
+    title: String,
+    symbol: String?,
+    tint: Color = .gray900,
+    isUserInteractionEnabled: Bool = false,
+    duration: ToastTime = .medium
+  ) {
+    toasts.append(.init(title: title, symbol: symbol, tint: tint, isUseInteractionEnabled: isUserInteractionEnabled, duration: duration))
+  }
+}

Shared/Sources/DesignSystem/Components/Toast/ToastItem.swift

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+//
+//  ToastItem.swift
+//
+//
+//  Created by 홍승현 on 3/24/24.
+//
+
+import SwiftUI
+
+// MARK: - ToastItem
+
+struct ToastItem: Identifiable {
+  let id: UUID = .init()
+
+  // MARK: Custom Properties
+
+  /// 토스트 제목
+  let title: String
+
+  /// 토스트 심볼 이미지 문자열
+  let symbol: String?
+
+  /// 토스트 틴트 색상
+  let tint: Color
+
+  /// 사용자 상호작용 여부
+  let isUseInteractionEnabled: Bool
+
+  // MARK: Timing
+
+  /// 토스트 유지 시간
+  let duration: ToastTime
+
+  init(title: String, symbol: String?, tint: Color, isUseInteractionEnabled: Bool, duration: ToastTime) {
+    self.title = title
+    self.symbol = symbol
+    self.tint = tint
+    self.isUseInteractionEnabled = isUseInteractionEnabled
+    self.duration = duration
+  }
+}
+
+// MARK: - ToastTime
+
+public enum ToastTime: CGFloat {
+  case short = 1.0
+  case medium = 2.0
+  case long = 3.5
+}

Shared/Sources/DesignSystem/Components/Toast/View/RootView.swift

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+//
+//  RootView.swift
+//
+//
+//  Created by 홍승현 on 3/24/24.
+//
+
+import SwiftUI
+
+// MARK: - RootView
+
+public struct RootView<Content: View>: View {
+  @ViewBuilder public var content: Content
+
+  @inlinable public init(@ViewBuilder content: @escaping () -> Content) {
+    self.content = content()
+  }
+
+  // MARK: View Properties
+
+  @State private var overlayWindow: UIWindow?
+
+  public var body: some View {
+    content
+      .onAppear {
+        for scene in UIApplication.shared.connectedScenes where scene.activationState == .foregroundActive && overlayWindow == nil {
+          if let windowScene = scene as? UIWindowScene {
+            let window = PassthroughWindow(windowScene: windowScene)
+            window.backgroundColor = .clear
+            window.isUserInteractionEnabled = true
+            window.isHidden = false
+
+            // view controller part
+
+            let rootController = UIHostingController(rootView: ToastGroup())
+            rootController.view.frame = windowScene.screen.bounds
+            rootController.view.backgroundColor = .clear
+            window.rootViewController = rootController
+
+            overlayWindow = window
+            break
+          }
+        }
+      }
+  }
+}
+
+// MARK: - PassthroughWindow
+
+private class PassthroughWindow: UIWindow {
+  override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
+    guard let view = super.hitTest(point, with: event) else { return nil }
+    return rootViewController?.view == view ? nil : view
+  }
+}

Shared/Sources/DesignSystem/Components/Toast/View/ToastGroup.swift

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+//
+//  ToastGroup.swift
+//
+//
+//  Created by 홍승현 on 3/24/24.
+//
+
+import SwiftUI
+
+struct ToastGroup: View {
+  let model = Toast.shared
+  var body: some View {
+    GeometryReader { proxy in
+      let size = proxy.size
+      let safeArea = proxy.safeAreaInsets
+
+      ZStack {
+        ForEach(model.toasts) {
+          ToastView(size: size, item: $0)
+        }
+      }
+      .padding(.bottom, safeArea.top == .zero ? 15 : 10)
+      .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .bottom)
+    }
+  }
+}

Shared/Sources/DesignSystem/Components/Toast/View/ToastView.swift

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+//
+//  ToastView.swift
+//
+//
+//  Created by 홍승현 on 3/24/24.
+//
+
+import SwiftUI
+
+struct ToastView: View {
+  var size: CGSize
+  var item: ToastItem
+
+  var body: some View {
+    HStack(spacing: 0) {
+      if let symbol = item.symbol {
+        Image(systemName: symbol)
+          .font(.title3)
+          .padding(.trailing, 10)
+      }
+
+      Text(item.title)
+    }
+    .foregroundStyle(item.tint)
+    .padding(.horizontal, 15)
+    .padding(.vertical, 8)
+    .background(
+      .background
+        .shadow(.drop(color: .primary.opacity(0.06), radius: 5, x: 5, y: 5))
+        .shadow(.drop(color: .primary.opacity(0.06), radius: 5, x: -5, y: -5)),
+      in: .capsule
+    )
+    .contentShape(.capsule)
+  }
+}