Handle `SIGTTOU` when switching to cooked mode on Unix about cathode

[alexrp]

One option would be to compare the current termios values to our desired values and only call tcsetattr if they differ.

The obvious downsides here are:

• It'll be a bit messy since we only want to compare well-known bits, not entire fields.
• It might not even help most of the time since it seems that our desired values differ slightly from the default values on both Linux and macOS (in different ways).

[alexrp]

But what about the times when the foreground process is in raw mode and we end up completely garbling the screen?

Such an application should really set TOSTOP (which we would be forced to respect as we can't block/ignore SIGTTOU from managed land anyway). See:

• #48

[alexrp]

I think I'm satisfied that there would be no major issues with just assuming we're in cooked mode. I think it's entirely reasonable to say that if a parent process launches a child process in raw mode, the developer of the parent process is doing it wrong. Nobody expects their program to launch in raw mode.