Migrate to ESM with esbuild and vitest (#243)

* Migrate to ESM with esbuild, vitest and upgrade @actions/* to ESM-only versions

* fix: update lockfile for npm ci compatibility

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Co-authored-by: Suneha Bose <suneha.bose@gmail.com>

tsconfig.json

@@ -1,8 +1,12 @@
 {
    "compilerOptions": {
       "target": "ES2020",
-      "module": "commonjs",
-      "lib": ["ES2020", "DOM"]
+      "module": "NodeNext",
+      "moduleResolution": "NodeNext",
+      "rootDir": "./src",
+      "outDir": "./lib",
+      "skipLibCheck": true,
+      "noEmit": true
    },
-   "exclude": ["node_modules", "test"]
+   "exclude": ["node_modules", "**/*.test.ts", "vitest.config.ts"]
 }