Fix MainActor concurrency errors in HotReloadable macro output

Author: stackotter

Examples/Sources/CounterExample/CounterApp.swift

@@ -18,6 +18,7 @@ struct CounterApp: App {
                         count -= 1
                     }
                     Text("Count: \(count)")
+                        .foregroundColor(.red)
                     Button("+") {
                         count += 1
                     }

Sources/HotReloadingMacrosPlugin/HotReloadableAppMacro.swift

@@ -20,6 +20,7 @@ extension HotReloadableAppMacro: PeerMacro {
                 var hotReloadingImportedEntryPoint: (@convention(c) (UnsafeRawPointer, Int) -> Any)? = nil
                 """,
                 """
+                @MainActor
                 @_cdecl("body")
                 public func hotReloadingExportedEntryPoint(app: UnsafeRawPointer, viewId: Int) -> Any {
                     hotReloadingHasConnectedToServer = true