cli: use a "leftward harpoon over rightward harpoon" for elided nodes

[thoughtpolice]

This is just an experiment to see how a new elided node looks. I like the feature, but I think the text is a little hard to see due to the lack of surrounding whitespace; having a more distinct marker might help split the difference.

Also, the existing pick, DOTTED CIRCLE, seen as ◌, sometimes renders very poorly in certain fonts, depending on a number of factors. I think a contributing factor is that not all fonts have monospace unicode characters for this block of characters; it also seems as if DOTTED CIRCLE is not in the same "logical group" of characters in that block that includes our lovely ◉, which is FISHEYE. Maybe another ... CIRCLE character would be better, but the ones close by don't seem too great for this purpose.

Instead, this picks a completely distinct character, using LEFTWARD HARPOON OVER RIGHTWARD HARPOON, seen as ⇋ to mark elided nodes, since it kind of reminded me of a "scissor snip", removing the middle of a string, or something.

To keep a similar visual language, = is used in ASCII.

I've been running this for a week or so, and I quite like it. But I figured I'd put it up here in case anyone else wants to try it. We could also make it configurable, but maybe this could be a better default? I'm not sure. We'd have to get people to try it.

Here is an example from my inline VS Code terminal, using PragmataPro Mono:

[NoahTheDuke]

I like it

[ilyagr]

This makes me think about using ~ if we can't use the dotted circle. The harpoons look a little busy by comparison. I think they are fine, though.

At some point, I guess we can have various themes for the graph :)

[thoughtpolice]

This was obsoleted via #3263, so closing. You can use whatever node you want now. :)