feat: Add expression evaluation back to REPL

[danvk]

This is chapter 8 challenge 1. This is a case where using a class for the parser would be helpful, since it would be easier to make both the parse and expression methods public.

I'm following the Node readline tiny CLI example: https://nodejs.org/api/readline.html#example-tiny-cli

It's nice to have up arrow in the CLI, but there's definitely a flicker that I don't love.

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[codecov]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (d610476) 96.18% compared to head (97aabdc) 96.33%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
src/main.ts	78.72%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #18      +/-   ##
==========================================
+ Coverage   96.18%   96.33%   +0.15%     
==========================================
  Files          11       11              
  Lines         995     1036      +41     
  Branches      147      155       +8     
==========================================
+ Hits          957      998      +41     
  Misses         37       37              
  Partials        1        1              

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