migrate to "export default"

also, set no-use-before-define in linter

src/test/syncer-test.js

@@ -1,6 +1,6 @@
 /* global it:false */
 
-import * as common from './common.js';
+import common from './common.js';
 const { createTree } = common;
 import DataLayout from '../datalayout.js';
 import { execSync } from 'node:child_process';
@@ -10,7 +10,7 @@ import os from 'node:os';
 import path from 'node:path';
 import paths from '../paths.js';
 import safe from 'safetydance';
-import * as syncer from '../syncer.js';
+import syncer from '../syncer.js';
 
 /* global describe:false */
 /* global before:false */