Add option for a prompt on the CLI

[gussmith23]

I'm working on a project that interacts with egglog's CLI programmatically. Being able to detect when a command is done is useful. A prompt is a very easy way to detect when a command completes.

This trips the nits detector because of the use of print! -- can I get around that somehow?

[codspeed-hq]

CodSpeed Performance Report

Merging #518 will not alter performance

_{Comparing gussmith23:gussmith23-prompt (d253ec6) with main (215714e)}

Summary

✅ 10 untouched benchmarks

[yihozhang]

The interactive mode will print a (done) once every command is done (sorry for the poor documentation). Does that work for you?

[gussmith23]

The interactive mode will print a (done) once every command is done (sorry for the poor documentation). Does that work for you?

Unfortunately no -- here's why. My interactive routine needs to be able to run multiple commands at once, and only have a single prompt/marker appear at the very end of all of the commands. Currently, I do this by writing a batch of commands to a file and then using (include <filepath>). Because include is just a single command at the top level, all of the commands in the file will run and a single prompt will be printed when they're all done. Based on my testing, interactive mode prints a (done) after each command, even if the commands were included. This is an issue, because if I don't know how many commands were in the included file, I don't know how many (done)s to look for. With the prompt, however, I always know to look for a single prompt at the very end.