Migrate to ESM with esbuild/vitest and upgrade to node24 (#260)

- Add "type": "module" to package.json for ESM support
- Replace ncc with esbuild for bundling (with createRequire banner for CJS compat)
- Replace jest/ts-jest with vitest for testing
- Upgrade @actions/core to ^3.0.0, @actions/exec to ^3.0.0, @actions/io to ^3.0.2, @actions/tool-cache to 4.0.0 (ESM-only versions)
- Update tsconfig.json to use NodeNext module resolution
- Convert all tests to use vi.mock() factory pattern for ESM-only module compatibility
- Update action.yml runtime from node20 to node24
- Bump version from 4.3.1 to 5.0.0 (major version bump for breaking node runtime change)

package.json

@@ -5,31 +5,31 @@
    "description": "Setup helm",
    "author": "Anumita Shenoy",
    "license": "MIT",
+   "type": "module",
    "dependencies": {
-      "@actions/core": "^2.0.2",
-      "@actions/exec": "^2.0.0",
-      "@actions/io": "^2.0.0",
-      "@actions/tool-cache": "3.0.0",
+      "@actions/core": "^3.0.0",
+      "@actions/exec": "^3.0.0",
+      "@actions/io": "^3.0.2",
+      "@actions/tool-cache": "4.0.0",
       "@octokit/action": "^8.0.4",
       "semver": "^7.7.3"
    },
    "main": "lib/index.js",
    "scripts": {
-      "build": "ncc build src/index.ts -o lib",
-      "test": "jest",
-      "test-coverage": "jest --coverage",
+      "build": "tsc --noEmit && esbuild src/index.ts --bundle --platform=node --target=node20 --format=esm --outfile=lib/index.js --banner:js=\"import { createRequire } from 'module';const require = createRequire(import.meta.url);\"",
+      "typecheck": "tsc --noEmit",
+      "test": "vitest run",
+      "test-coverage": "vitest run --coverage",
       "format": "prettier --write .",
       "format-check": "prettier --check .",
       "prepare": "husky"
    },
    "devDependencies": {
-      "@types/jest": "^30.0.0",
       "@types/node": "^25.0.9",
-      "@vercel/ncc": "^0.38.4",
+      "esbuild": "^0.27",
       "husky": "^9.1.7",
-      "jest": "^30.2.0",
       "prettier": "^3.8.0",
-      "ts-jest": "^29.4.6",
-      "typescript": "^5.9.3"
+      "typescript": "^5.9.3",
+      "vitest": "^4"
    }
 }