Figure out better (i.e. more testable) way to load axe.js in cli

[straker]

Currently the cli tries to load axe.js from 3 different locations (in oder):

1. process.cwd()
2. process.cwd() node_modules
3. the cli's node_modules

The problem is that this makes it really hard to test. We were using fs-mock but then ran into a problem in node v20.5.0 that prevented fs-mock from working. So we converted our small use case from fs-mock to use tempy, but that required a small hack to allow passing in what the process.cwd was, and trying to mock out what the cli's node_modules was.

I think we should spend some time thinking about how to write the code to be more easily testable. Right now it requires the hack to define what the working directory and file directory is. It also is highly dependent on how the final code is built (/dist/src/lib), but changing our build process shouldn't break our code.