Use splice to pump tty to avoid userspace copying

[yujincheng08]

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[Copilot]

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native/src/core/su/pts.rs:149

• The usage of size_of here requires an explicit import; consider adding 'use std::mem::size_of' at the top of the file.

let mut buf: [MaybeUninit<u8>; size_of::<signalfd_siginfo>()] = MaybeUninit::uninit_array();