ci: serialize test files to avoid parallel dist/ build races

Multiple suites (cli.subprocess, help.snapshot, credentials lock) each run
npm run build in beforeAll. With fileParallelism enabled, workers can corrupt
dist/ mid-run and subprocess smoke tests flake with exit 1. Run build once in
CI before npm test and disable vitest file parallelism.

Author: SahilRakhaiya05

.github/workflows/ci.yml

@@ -55,6 +55,7 @@ jobs:
           cache: 'npm'
 
       - run: npm ci
+      - run: npm run build
       - run: npm test
         env:
           CI: true

vitest.config.ts

@@ -4,6 +4,9 @@ export default defineConfig({
   test: {
     include: ['src/**/*.{test,spec}.ts', 'test/**/*.{test,spec}.ts'],
     exclude: ['test/dev-e2e/**', 'test/e2e/**', 'node_modules/**', 'dist/**'],
+    // Subprocess/snapshot suites each run `npm run build` in beforeAll; parallel
+    // file workers can race on dist/ and produce a stale binary (exit 1 vs 5 flakes).
+    fileParallelism: false,
     coverage: {
       provider: 'v8',
       reporter: ['text', 'text-summary', 'json-summary', 'html'],