[feature request] fixed size terminals (eg. 80x24)

I often SSH into my libvirt/KVM host, and then access guest systems using `virsh console `. In this case, using a terminal size of 80x24 characters is required or weird things can happen. On my Mac, I can easily set my terminal to be exactly 80x24 for this purpose, however this is not the case with Blink (or any other mobile SSH client I've used before).

While a possible workaround for this would be prefixing commands with `COLUMNS=80 LINES=24`, a much more elegant solution would be allowing the user to set a fixed terminal size. In this case, Blink could scale the terminal to best fit the screen, rather than leaving blank space around those 80 columns and 24 lines.

Start by tracing how Blink determines the terminal size when using `virsh console ` and compare it with the `COLUMNS=80 LINES=24` workaround. The feature would be complete when users can choose a fixed 80x24 terminal and Blink scales it to the screen without leaving unnecessary blank space.

Written by the indexing model from the issue text.