Migrate to esbuild/Vitest and upgrade @actions/* to ESM-only versions (#492)

* Migrate build toolchain from ncc/Jest to esbuild/Vitest

Replace the legacy ncc/Jest/Babel build stack with a modern ESM toolchain:

Build:
- Replace @vercel/ncc with esbuild (--platform=node --target=node20 --format=esm)
- Add createRequire banner for CJS interop in ESM bundle
- Add "type": "module" to package.json
- Add tsc --noEmit typecheck script (esbuild strips types without checking)
- Add typecheck to husky pre-commit hook

Dependencies:
- Bump @actions/core@3, exec@3, io@3, tool-cache@4 (ESM-only)
- Replace jest/ts-jest/@babel/* with vitest@4

Tests:
- Convert 29 test files: jest.fn()→vi.fn(), jest.mock()→vi.mock(), jest.spyOn()→vi.spyOn()
- Fix vitest 4 compat: mockImplementation requires args, mock call tracking, await .rejects

CI:
- Update build step from ncc build → npm run build
- Update composite action to use npm run build

* Switch tsconfig to NodeNext module resolution

Change module/moduleResolution from ES2022/bundler to NodeNext/NodeNext
and target from ES2022 to ES2020.

- Add .js extensions to all relative imports across 59 source/test files
  (required by NodeNext module resolution)
- Add vitest/globals to tsconfig types array for global test API declarations

src/utilities/fileUtils.test.ts

@@ -1,9 +1,10 @@
-import * as fileUtils from './fileUtils'
+import {vi} from 'vitest'
+import * as fileUtils from './fileUtils.js'
 
 import * as yaml from 'js-yaml'
 import fs from 'node:fs'
 import * as path from 'path'
-import {K8sObject} from '../types/k8sObject'
+import {K8sObject} from '../types/k8sObject.js'
 
 const sampleYamlUrl =
    'https://raw.githubusercontent.com/kubernetes/website/main/content/en/examples/controllers/nginx-deployment.yaml'
@@ -69,7 +70,7 @@ describe('File utils', () => {
          'manifest_test_dir'
       )
 
-      expect(
+      await expect(
          fileUtils.getFilesFromDirectoriesAndURLs([badPath, goodPath])
       ).rejects.toThrow()
    })
@@ -108,8 +109,8 @@ describe('File utils', () => {
 
 describe('moving files to temp', () => {
    it('correctly moves the contents of a file to the temporary directory', () => {
-      jest.spyOn(fs, 'writeFileSync').mockImplementation(() => {})
-      jest.spyOn(fs, 'readFileSync').mockImplementation((filename) => {
+      vi.spyOn(fs, 'writeFileSync').mockImplementation(() => {})
+      vi.spyOn(fs, 'readFileSync').mockImplementation((filename) => {
          return 'test contents'
       })
       const originalFilePath = path.join('path', 'in', 'repo')