Add support for `lang` attribute

[jasikpark]

In astro, you can add a lang attribute to change the way that the style tag is parsed.

https://docs.astro.build/en/guides/styling/#css-preprocessors

it'd be great to have those files parsed as different languages / extensions depending on the option

I'm not sure how this could be hooked exactly, it might be best to just choose a single styling language for astro inline styles