`MapContent` ignores `@Observable` updates – not aligned with SwiftUI expectations

Nobody has claimed this yet.

## Environment

- Xcode version: 16.4
- iOS version: 18.6
- Devices affected: any
- Maps SDK Version: 11.14.0

## Observed behavior and steps to reproduce

MapContent does not react to `@Observable` state updates. Here's the minimal test case:

```swift

@Observable
class TestViewModel {
var pluckBearing = false
}

struct MapTestContent: MapContent {
let viewModel: TestViewModel

var body: some MapContent {
if viewModel.pluckBearing {
Puck2D(bearing: .heading)
} else {
Puck2D(bearing: .none)
}
}
}

struct MapTest: View {
let viewModel = TestViewModel()

var body: some View {
VStack {
Map {
MapTestContent(viewModel: viewModel)
}

Button("Toggle Puck Bearing") {
viewModel.pluckBearing.toggle()
}
}
}
}
```

Tapping the button has currently no effect.

## Expected behavior

Tapping the button should update pluck style. So, I'd expect `MapContent` get re-evaluated when `@Observable` state is updated.

## Notes / preliminary analysis

The ability to update only the leaf nodes of the map declaration tree could lead to significant performance improvements.

Start with the minimal MapTestContent reproduction in the issue and inspect the MapContent evaluation and observation entry points. Confirm the behavior on the stated Xcode 16.4, iOS 18.6, and Maps SDK 11.14.0 environment; done means toggling pluckBearing updates the Puck2D style without rebuilding unrelated map content.

Written by the indexing model from the issue text.