[Virtio-fs] [virtiofsd-rs] MR opened: Add --inode-file-handles=mandatory

[virtiofs-bot at sinrega.org]

In this mode, we never fall back to opening an `O_PATH` file descriptor to keep in our `InodeData` objects, but instead return all `name_to_handle_at()` errors to the guest.
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https://gitlab.com/virtio-fs/virtiofsd/-/merge_requests/59