Migrate to ESM and upgrade dependencies (#752)

* Migrate to ESM and upgrade dependencies

* Address review: use type-only import for QualityOptions

* update version to 6.0.0 in package.json and package-lock.json

* Add ESM migration note to README for V6

* Update test imports for ESM and clean up devDependencies (ts-node, @types/jest)

* Pin @types/node to 24.x and refine tsconfig/README wording

jest.config.ts

@@ -0,0 +1,28 @@
+import type {JestConfigWithTsJest} from 'ts-jest';
+
+const jestConfig: JestConfigWithTsJest = {
+  clearMocks: true,
+  testEnvironment: 'node',
+  moduleFileExtensions: ['js', 'ts'],
+  testMatch: ['**/*.test.ts'],
+  testRunner: 'jest-circus/runner',
+  extensionsToTreatAsEsm: ['.ts'],
+  moduleNameMapper: {
+    '^(\\.{1,2}/.*)\\.js$': '$1'
+  },
+  transform: {
+    '^.+\\.ts$': [
+      'ts-jest',
+      {
+        useESM: true,
+        diagnostics: {
+          ignoreCodes: [151002]
+        }
+      }
+    ]
+  },
+  transformIgnorePatterns: ['node_modules/(?!(@actions)/)'],
+  verbose: true
+};
+
+export default jestConfig;