Refactor a smidge, so that future PRs can better build off the smaller methods

[NullVoxPopuli]

... and we don't end up with a mega method.

This is required for #8 and is the main blocker to reviewing #8

Commits are atomic, so reviewing per commit may be benificial

[mansona]

I'm closing this for now. Please see my last two comments in https://github.com/mainmatter/ember-asset-size-action/pull/8#issuecomment-1483925491 for an explanation 👍