Migrate to ESM and upgrade dependencies (#763)

* Migrate to ESM and upgrade dependencies

* Remove unused tsconfig.eslint.json

* bump version to 7.0.0 in package.json and package-lock.json

* Add ESM migration note to README for V7

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

* npm audit fix

* Update README with ESM migration details

Clarified migration details to ESM for action compatibility.

* Downgrade @types/node to ^24, clean up tsconfig and README.

src/cache-utils.ts

@@ -1,7 +1,10 @@
 import * as cache from '@actions/cache';
 import * as core from '@actions/core';
 import * as exec from '@actions/exec';
-import {supportedPackageManagers, PackageManagerInfo} from './package-managers';
+import {
+  supportedPackageManagers,
+  PackageManagerInfo
+} from './package-managers.js';
 
 export const getCommandOutput = async (toolCommand: string) => {
   let {stdout, stderr, exitCode} = await exec.getExecOutput(