[net] add explicit lifetime to tcp socket split() function

[siemtim-dev]

I added explicit lifetimes to the TcpSocket::split() function.

old version:

    pub fn split(&mut self) -> (TcpReader<'_>, TcpWriter<'_>) {
        (TcpReader { io: self.io }, TcpWriter { io: self.io })
    }

In the old version the lifetime of the TcpReader and TcpWriter seems to be the lifetime of &mut self. By adding explicit lifetimes users of this function have more flexibility.

What do you think about this change?

[Dirbaio]

this would allow multiple writers or readers existing for the same socket at the same time. The current signature of split() is intentionally designed to avoid this.

What are you trying to do that requires this change? maybe there's an alternate way.