fix: update lint script to use .ts extension and enhance package command

- Changed the lint script to specify the .ts extension explicitly.
- Modified the package script to run pretest before packaging with vsce.
- Added @vscode/test-cli as a dependency.

Author: mshr-h

.vscode-test.mjs

@@ -0,0 +1,5 @@
+import { defineConfig } from '@vscode/test-cli';
+
+export default defineConfig({
+	files: 'out/test/**/*.test.js',
+});