macos support: libc::pipe2 -> std::io::pipe

[S1M0N38]

I've try to compile tau on MacOS machine but macos does not support libc::pipe2. I've asked pi to fix:

https://pi.dev/session/#339a678ca2bf6301cbcfbf0a18f15b9a

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btw nice project :) I really like the concept of just having super minimal CLI (I love the fzf integration - I hate the @) I found out about it on yt. Coincidentally, I've worked on a tmux setup to help mange Pi coding agent which is named tau too. lol.