convert uses of `io.Pipe` to `cmd.Pipe*()`

Created by: camdencheek

There's this great footgun with go subprocesses where, if you use a non-file io.Writer for cmd.Stdout (and Stdin, and Stderr), it spins up a goroutine that reads from the OS pipe and writes to the writer. Additionally, cmd.Wait will not complete until that goroutine completes writing the output of your subcommand. Couple this with a synchronous io.Pipe, and cmd.Wait might never return.

This commit fixes an issue where, in some cancellation situations, there would be a goroutine leak because of this. Instead of io.Pipe, we use os.Pipe, which is what those above-mentioned background goroutines use behind the scenes anyways. This allows us to control the lifetime of the pipe.

Stacked on #25616