`cubecl::wgpu::GraphicsApi` returns non-reexported type `Backend`

[metasim]

GraphicsApi::backend() returns wgpu::Backend, which is not re-exported. In cases where type inference is not available, users of the return value will have to separately add a dependency on wgpu a manually keep the version up to date with cubecl:

cubecl/crates/cubecl-wgpu/src/graphics.rs

Lines 1 to 12 in b9fe581

	/// The basic trait to specify which graphics API to use as Backend.
	///
	/// Options are:
	/// - [Vulkan](Vulkan)
	/// - [Metal](Metal)
	/// - [OpenGL](OpenGl)
	/// - [DirectX 12](Dx12)
	/// - [WebGpu](WebGpu)
	pub trait GraphicsApi: Send + Sync + core::fmt::Debug + Default + Clone + 'static {
	/// The wgpu backend.
	fn backend() -> wgpu::Backend;
	}

Proposed fix would be to add pub use wgpu::Backend to graphics.rs.