Add support for DECSCUSR (Set Cursor Style)

[reubeno]

This set of changes adds support for DECSCUSR (CSI Ps SP q):

• ESC [ 0 ␣ q - terminal default
• ESC [ 1 ␣ q - blinking block
• ESC [ 2 ␣ q - steady block
• ESC [ 3 ␣ q - blinking underline
• ESC [ 4 ␣ q - steady underline
• ESC [ 5 ␣ q - blinking bar
• ESC [ 6 ␣ q - steady bar

I've tried to model the code changes on how mouse modes are currently implemented, as this seemed like a natural analogue. I see that cursor hiding is represented as mode bits, but this didn't seem to be fit well with that.

(This is my first contribution to this project, so I'd appreciate any pointers for additional tests I should be authoring or other consideration. Thanks!)

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References

• https://vt100.net/docs/vt510-rm/DECSCUSR.html
• https://terminalguide.namepad.de/seq/csi_sq_t_space/
• https://learn.microsoft.com/en-us/windows/console/console-virtual-terminal-sequences
• https://ghostty.org/docs/vt/csi/decscusr