test(integration): pin prototype-method-resolution test to WASM engine

The test was using auto engine (native-preferred), causing it to pick the
published npm native binary which predates the prototype-method fixes.
WASM correctly extracts Dog.prototype.bark and resolves all call edges.

Fixes #1381

Author: carlos-alm

tests/integration/prototype-method-resolution.test.ts

@@ -48,7 +48,7 @@ beforeAll(async () => {
   for (const [rel, content] of Object.entries(FIXTURE)) {
     fs.writeFileSync(path.join(tmpDir, rel), content);
   }
-  await buildGraph(tmpDir, { incremental: false, skipRegistry: true });
+  await buildGraph(tmpDir, { incremental: false, skipRegistry: true, engine: 'wasm' });
 });
 
 afterAll(() => {