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/custom_op.rs

@@ -386,6 +386,7 @@ pub struct UgIOp1 {
 
 impl UgIOp1 {
     #[allow(unused)]
+    #[cfg(not(target_arch = "wasm32"))]
     pub fn new(
         name: &'static str,
         kernel: ug::lang::ssa::Kernel,