os.pipe on windows and seekable

[braingram]

On windows, os.pipe produces a file object that reports as seekable but cannot be seeked (tell is always 0, seek does nothing). This is a reported issue in python since 3.8:
https://bugs.python.org/issue42602

The implications for asdf should be determined. I expect that write will produce an invalid block index (due to tell reporting 0) and read and update will fail (as they will attempt to seek).