Turbopack: Add a stress test / fuzzer that tries creating many symlinks in a tight loop #88667
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…80 on Windows (#88669) Though I've been unable to reproduce the issue (prior PRs in this stack are my attempts at that), I believe this *should* fix the OS Error 80 ([`ERROR_FILE_EXISTS`](https://learn.microsoft.com/en-us/windows/win32/debug/system-error-codes--0-499-)) that we've seen users report on Windows: #88382 Basically instead of deleting the existing link in a retry loop, and then trying to create new new link using a retry loop, we should instead: - Merge these two retry loops into one, in case another process creates the link after we delete it. This shouldn't typically happen, but could theoretically happen. - Extend the retry logic to also retry on [`ErrorKind::AlreadyExists`](https://github.com/rust-lang/rust/blob/503745e9170b40841611aaaa634641edffd00b29/library/std/src/sys/io/error/windows.rs#L19). This might be possible if the filesystem is eventually consistent (which can happen on Windows), but I wasn't able to reproduce this. There's a similar -- but different -- issue that users have been reporting where they get OS Error 1 (`ERROR_INVALID_FUNCTION`) on Windows. I believe this happens if we try to create a junction point on a non-NTFS filesystem. In that case, we need to report a clearer issue to the user instead of bubbling this up as an internal Turbopack error. I tested this on Windows with the symlink fuzzer from #88667, as well as `cargo test -p turbo-tasks-fs`: 
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In an attempt to reproduce #88382, this tries creating and updating a bunch of symlinks/junction points in a tight loop with some parallelism. However, I've been unable to reproduce the error reported in that discussion.
I don't care about the code quality here, so this was LLM-generated with very lightweight review.
A simplified version of the fuzzer is also included as a unit test in
turbo-tasks-fs. This version only does a few iterations and runs very quickly.