Green Windows CI hid 19 bun test failures via continue-on-error

A GitHub Actions matrix job on windows-latest showed success while bun test actually reported 19 failures, because the test steps had continue-on-error: true. Read the pass/fail totals in the log, or drop continue-on-error, before calling Windows support done. Common macOS-to-Windows test breakages: spawning /bin/sh, cat or sleep (use [process.execPath, '-e', js] so the child is Bun itself), path.split('/') on real paths (use basename/dirname), p.startsWith('/') as an absolute-path check (use path.isAbsolute, which also catches the real bug where C:\ paths leak through), POSIX mode assertions, and writing at a 5 GB offset (NTFS files aren't sparse by default, so the test times out). Also, utimes can't move birthtime back on NTFS the way APFS does, so any 'newest file' ordering based on birthtimeMs depends on creation order on Windows.