improve experimental broken pipe logging testing

[garypen]

The tests are marked as flaky in CI, so let's try to improve them.

• Reduce the timeout (nano-seconds rather than micro-seconds)
• Remove the (seemingly) redundant sleep
• Make the test multi-threaded (which I think it should be)
• Add comments to explain what the tests are doing

[github-actions[bot]]

@garypen, please consider creating a changeset entry in /.changesets/. These instructions describe the process and tooling.

[BrynCooke]

This is the number one test that seems to flake for me.