dev-cmd/audit: fix cask arg handling

[Rylan12]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew typecheck with your changes locally?
• Have you successfully run brew tests with your changes locally?

---

This fixes an issue where brew audit --cask --new-cask did not run the check_token_conflicts check as it should have. This was because at some point in the past, args.token_conflicts? started returning true/false instead of true/nil. Since false.nil? is false but false.blank? is true, this wasn't triggering properly. There are a few other implied audit rules that likely were affected as a result of this. that I've fixed here, too.

[BrewTestBot]

Review period ended.

[Rylan12]

I realized that it is valuable to have a distinction between nil and false for testing. That way, false means "this is 100% false never set it to true" and nil means "unset so make whatever changes are needed."

Now, we can set new_cask to true while keeping online off. Before, setting online to false was treated as if --online wasn't passed (because there's no --no-online flag) and so the --new was overriding the value set in the test.

Instead, we handle the change in the brew audit command, itself, by adding || nil to pass nil (i.e. "unset") to the auditor whenever args.foo? returns false.

In other words, the argument parser returns false when a (non-boolean) switch isn't set, and the auditor expects nil to mean unset. So, we change falses to nils before passing them.

---

--[no-]appcast is excluded from all of the above because the argument parser already returns nil/false/true because it's a boolean switch.