SwiftUI RasterSource doesn't allow expected use of `.scheme` property

Nobody has claimed this yet.

## Environment

- Xcode version: Version 16.0 (16A242d)
- iOS version: 17.5.1
- Devices affected: Any - it's a compilation issue
- Maps SDK Version: 11.7.1

## Observed behavior and steps to reproduce

Trying to set the `.scheme` property as normal gives a compiler error as shown:


As I workaround, I can do this instead:

```
import SwiftUI
import MapboxMaps
import DerivedStateProvider

import DesignSystem

struct WeatherMap: View {
@Environment(WeatherModuleViewModel.self) var viewModel

let source: RasterSource = {
var source = RasterSource(id: "weather-test")
source.scheme = .tms // workaround - set scheme property here
return source
}()

public init() {}

var body: some View {

@Bindable var module = viewModel.moduleState

VStack {
Map(initialViewport: .camera(center: self.viewModel.preset.primaryPin.coordinate, zoom: 6, bearing: 0, pitch: 0)) {

if module.tileURLTemplate != nil {
source
.maxzoom(16)
.minzoom(1)
.tileNetworkRequestsDelay(200)
.tiles([module.tileURLTemplate!])

RasterLayer(id: "weather-test-layer", source: "weather-test")
.rasterOpacity(0.8)
}
}.ignoresSafeArea()
}
}
}
```

## Expected behavior

`.scheme` should be settable as expected inline as follows:

```
RasterSource(id: "weather-test")
.maxzoom(16)
.minzoom(1)
.tileNetworkRequestsDelay(200)
.tiles([module.tileURLTemplate!])
.scheme(.tms)
```

## Notes / preliminary analysis

Unclear why this is different - the property appears to be declared in a similar fashion to the others, e.g.

```
/// A raster tile source.
///
/// - SeeAlso: [Mapbox Style Specification](https://docs.mapbox.com/mapbox-gl-js/style-spec/sources/#raster)
public struct RasterSource: Source {

public let type: SourceType
public let id: String

...

/// Minimum zoom level for which tiles are available, as in the TileJSON spec.
/// Default value: 0.
public var minzoom: Double?

...

/// Influences the y direction of the tile coordinates. The global-mercator (aka Spherical Mercator) profile is assumed.
/// Default value: "xyz".
public var scheme: Scheme?

...
}
```

Here's what Claude had to say:

> Given what we discovered, it seems like there's a mismatch in how MapBox implemented their SwiftUI property wrappers. Let me break down what I think might be happening:
>
> - Most of the properties (like maxzoom, minzoom, etc.) are properly wrapped with SwiftUI property modifiers that create method-style chainable modifiers (that's why they work with the .maxzoom(16) syntax and show up in teal)
> - But scheme seems to have been missed in this wrapper layer (showing up in purple), suggesting it's being exposed directly as a Swift property rather than being wrapped in the SwiftUI modifier pattern
>
> This is particularly evident because:
>
> - We couldn't use .scheme(.tms) like the other modifiers
> - We had to set it directly on the source instance
> - The direct property is marked as Scheme? in the header but the modifier system wasn't handling that optional type correctly
>
> This kind of inconsistency often happens when building SwiftUI wrappers around existing UIKit/imperative APIs, especially if some properties are auto-generated or wrapped automatically while others need manual handling.

The issue identifies RasterSource and the working maxzoom, minzoom, tileNetworkRequestsDelay, and tiles modifier chain, but no repository file or test. Start by locating the SwiftUI source declaration and comparing how scheme is exposed with those modifiers. Done means RasterSource accepts inline .scheme(.tms) chaining without the workaround and the example compiles.

Written by the indexing model from the issue text.