fix: place ug dep behind not wasm32 flag (#2760)

* place `ug` behind not wasm32 attr

so that wasm32 can compile

* mv `ug` to conditional target dep

assuming every non-wasm32 user wants this

candle-core/src/metal_backend/device.rs

@@ -138,6 +138,7 @@ impl std::ops::Deref for MetalDevice {
 }
 
 impl MetalDevice {
+    #[cfg(not(target_arch = "wasm32"))]
     pub fn compile(
         &self,
         func_name: &'static str,