Make client more ESM-friendly (#2348)

* Use node: prefix for stdlib imports

* Make code more ESM-friendly

* Add missing mjs file

* Drop mjs file from package.json

test/unit/helpers/search.test.ts

@@ -108,4 +108,5 @@ test('Merge filter paths (snake_case)', async t => {
     { two: 'two' },
     { three: 'three' }
   ])
-})
+})
+