perf(cli): skip native-binary build tests by default

The build-exe and build-exe-cross suites invoke `bun build` in beforeAll
hooks and pegged CPU for ~6 min on every test run (one cached-on-miss
build plus three unconditional cross-target builds). Move them to a
dedicated vitest project, skip them unless CI=1 or FUSION_TEST_BUILD_EXE=1
is set, and add cache guards so CI re-runs skip rebuilds when the target
binary already exists. With build-exe out of the default cli run, the
main config can enable fileParallelism.

Run on demand via `pnpm --filter @runfusion/fusion test:build-exe`.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/cli/vitest.config.ts

@@ -23,6 +23,10 @@ export default defineConfig({
   },
   test: {
     include: ["src/**/*.test.ts"],
+    // build-exe + build-exe-cross live in their own vitest project
+    // (see vitest.build-exe.config.ts) so the rest of the CLI suite can
+    // run with file parallelism enabled.
+    exclude: ["**/node_modules/**", "**/dist/**", "src/__tests__/build-exe*.test.ts"],
     setupFiles: [
       "./src/__tests__/setup-test-isolation.ts",
       resolve(__dirname, "../core/src/__test-utils__/vitest-setup.ts"),
@@ -30,9 +34,7 @@ export default defineConfig({
     globalSetup: [resolve(__dirname, "../core/src/__test-utils__/vitest-teardown.ts")],
     maxWorkers,
     poolOptions: { threads: { minThreads: 1, maxThreads: maxWorkers }, forks: { minForks: 1, maxForks: maxWorkers } },
-    // build-exe and build-exe-cross suites both operate on packages/cli/dist/
-    // and can race when run in parallel workers.
-    fileParallelism: false,
+    fileParallelism: true,
     coverage: {
       enabled: false,
       reporter: ["text", "html", "json"],