Migrate to ESM with esbuild, vitest (#227)

* Migrate to ESM, esbuild, vitest, and update actions/* to latest

- Update @actions/core to 3.x, @actions/exec to 3.x, @actions/io to 3.x
- Replace @vercel/ncc + babel with esbuild (build.mjs) targeting Node 20 ESM
- Replace jest/babel-jest/ts-jest with vitest and @vitest/coverage-v8
- Update tsconfig to NodeNext module resolution with strict mode
- Add explicit .js extensions to all relative imports (NodeNext requirement)
- Fix implicit any index signatures in parseCluster and parseMethod
- Migrate all test files from jest to vi.mock/vi.mocked APIs
- Fix ESM module spying limitations using vi.mock() at module level
- Fix env var test pollution in default.test.ts with afterEach cleanup

* remove build.mjs and update build script

* update pkg lock

* update pkg lock

src/types/cluster.ts

@@ -8,9 +8,10 @@ export enum Cluster {
  * @param str The cluster type (case insensitive)
  * @returns The Cluster enum or undefined if it can't be parsed
  */
-export const parseCluster = (str: string): Cluster | undefined =>
-   Cluster[
-      Object.keys(Cluster).filter(
-         (k) => Cluster[k].toString().toLowerCase() === str.toLowerCase()
-      )[0] as keyof typeof Cluster
-   ]
+export const parseCluster = (str: string): Cluster | undefined => {
+   const key = Object.keys(Cluster).find(
+      (k) =>
+         Cluster[k as keyof typeof Cluster].toLowerCase() === str.toLowerCase()
+   ) as keyof typeof Cluster | undefined
+   return key !== undefined ? Cluster[key] : undefined
+}