fix(build): enable WASM features in wasm-opt optimization

ONNX Runtime builds WASM with bulk memory and non-trapping float-to-int
operations, but wasm-opt was running without these features enabled,
causing validation errors.

**Error:**
```
[wasm-validator error] memory.copy operations require bulk memory
operations [--enable-bulk-memory-opt]
[wasm-validator error] all used features should be allowed
(i32.trunc_sat_f64_s requires nontrapping-float-to-int)
```

**Fix:**
Add required feature flags to wasm-opt invocation:
- --enable-bulk-memory (for memory.copy, memory.fill)
- --enable-nontrapping-float-to-int (for i32.trunc_sat_*)
- --enable-sign-ext (for sign extension operations)

These are standard modern WASM features that ONNX Runtime uses
for better performance.

Author: jdalton

packages/build-infra/lib/emscripten-builder.mjs

@@ -112,7 +112,15 @@ export class EmscriptenBuilder {
 
     const result = await spawn(
       wasmOptCmd,
-      [`-O${optimizeLevel}`, '-s', shrinkLevel.toString(), wasmPath, '-o', wasmPath],
+      [
+        `-O${optimizeLevel}`,
+        '-s', shrinkLevel.toString(),
+        '--enable-bulk-memory',
+        '--enable-nontrapping-float-to-int',
+        '--enable-sign-ext',
+        wasmPath,
+        '-o', wasmPath
+      ],
       { shell: WIN32, stdio: 'inherit' }
     )
     if (result.code !== 0) {