Migrate to ESM and upgrade dependencies (#1330)

* Migrate to ESM and upgrade dependencies

* Add ESM migration note to README for V7

* Remove unnecessary devDependencies: ts-node, @types/jest

* npm audit fix

* Upgrade @types/node to version 26.0.0

* Clarify ESM migration details in README for V7

* Update README and dependencies

* Fix lint issue

src/find-pypy.ts

@@ -1,5 +1,5 @@
 import * as path from 'path';
-import * as pypyInstall from './install-pypy';
+import * as pypyInstall from './install-pypy.js';
 import {
   IS_WINDOWS,
   WINDOWS_ARCHS,
@@ -9,7 +9,7 @@ import {
   validatePythonVersionFormatForPyPy,
   IPyPyManifestRelease,
   getBinaryDirectory
-} from './utils';
+} from './utils.js';
 
 import * as semver from 'semver';
 import * as core from '@actions/core';