fix(@angular/build): prevent unit-test vitest runner from hanging after tests complete

[hebus]

PR Checklist

• The commit message follows our guidelines: https://github.com/angular/angular-cli/blob/main/CONTRIBUTING.md#-commit-message-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

• Bugfix

What is the current behavior?

In non-watch mode, ng test with the vitest runner hangs indefinitely after all tests
complete and results are printed. The executor disposes the Vitest instance with
close(), which has no teardown timeout. Whether the hang occurs depends on the size
of the TypeScript program of the spec tsconfig (full analysis in the linked issue) —
freshly generated projects exit cleanly while larger real-world projects hang on every
run, leaving orphaned node/esbuild processes in CI.

Issue Number: #32832 (likely also #33317)

What is the new behavior?

When not in watch mode, the executor calls vitest.exit() instead of vitest.close(),
mirroring what the vitest run CLI does: exit() arms an unref'd teardownTimeout
safety net (process.exit() after 10s by default) before closing. When teardown
completes normally nothing changes; when something keeps the event loop alive, vitest
reports it and force-exits:

close timed out after 10000ms
Tests closed successfully but something prevents the main process from exiting

Watch mode still uses close() and is unaffected.

Validated on a project that reproduces the hang on 100% of runs (315 tests, 19 spec files):

• run mode, passing tests: process now exits on its own, exit code 0
• run mode, failing tests: exit code 1 preserved
• watch mode: process stays alive, re-runs on change
• no orphaned node/esbuild processes after the run

Does this PR introduce a breaking change?

• No

Other information

No test added: asserting "the process exits" requires a real hanging handle, which the
builder test harness does not reproduce (small programs tear down cleanly — that is the
bug's timing dependency). Happy to add one if there is a suitable seam.

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[gemini-code-assist]

Code Review

This pull request updates the VitestExecutor disposal logic to call vitest.exit() instead of vitest.close() in non-watch mode, preventing hanging processes. The review feedback recommends adding a defensive check to verify that vitest.exit is a function before calling it, and warns that calling exit() could prematurely terminate the host process when executed programmatically.