fix: 🐛 Handle multiple Vue definitions/instances

If a file defines or instantiates more than one Vue component, and at least one of them has a render function/top-level template tag, the others which genuinely violate the rule were previously ignored.

Now, each Vue definition/instance in a file is inspected and reported on. There are probably still edge cases this doesn't catch, but for our purposes, it's good enough.

This is almost a breaking change, since potentially new violations would be found that weren't previously. Still, this is being considered as a bug in the original implementation rather than a breaking change.

✅ Closes: #25 (closed)