refactor: update imports to use ES module syntax and improve test structure (#1350)

- Changed import statements across multiple files to use the .js extension for ES module compatibility.
- Refactored test files to utilize jest's unstable_mockModule for mocking core actions.
- Removed unnecessary spy instances in tests, replacing them with direct mocked function calls.
- Updated TypeScript configuration to target ES2022 and use NodeNext module resolution.
- Removed the tsconfig.spec.json file and adjusted the main tsconfig.json to exclude test files.

jest.config.ts

@@ -0,0 +1,22 @@
+export default {
+  clearMocks: true,
+  moduleFileExtensions: ['js', 'ts'],
+  testMatch: ['**/*.test.ts', '**/*.spec.ts'],
+  transform: {
+    '^.+\\.ts$': [
+      'ts-jest',
+      {
+        useESM: true,
+        diagnostics: {
+          ignoreCodes: [151002]
+        }
+      }
+    ]
+  },
+  extensionsToTreatAsEsm: ['.ts'],
+  transformIgnorePatterns: ['node_modules/(?!(@actions|@octokit)/)'],
+  moduleNameMapper: {
+    '^(\\.{1,2}/.*)\\.js$': '$1'
+  },
+  verbose: true
+};