fix: checking unittest framework exists can be slow

Sometimes importing a test framework such as pytest can trigger
importing other code that has a longer runtime on import than allowed by
the spawned process. This fixes the issue by checking that the import
path can be found, which does not trigger importing the code.

src/commands.ts

@@ -11,7 +11,7 @@ const framework = workspace.getConfiguration('pyright').get<TestingFramework>('t
 
 function validPythonModule(pythonPath: string, moduleName: string) {
   try {
-    const pythonProcess = child_process.spawnSync(pythonPath, ['-m', moduleName, '--help'], { encoding: 'utf8' });
+    const pythonProcess = child_process.spawnSync(pythonPath, ['-c', `from importlib.machinery import PathFinder; assert PathFinder.find_spec("${moduleName}") is not None`], { encoding: 'utf8' });
     if (pythonProcess.error) return false;
     return pythonProcess.status === 0;
   } catch (ex) {