Compatibility with Tailwind 4.0.0-beta.5 and newer

Hi, I absolutely love this package and use it in all my projects. I also use Tailwind in all my projects. `postcss-advanced-variables` and Tailwind up to `4.0.0-beta.4` work perfectly together. However, since they've released `beta.5` this is no longer the case. I've opened an issue about it here: https://github.com/tailwindlabs/tailwindcss/discussions/15361

In the discussion, one of the Tailwind maintainers says that in order for these packages to work together again `postcss-advanced-variables` should be ported to use a `Once` visitor. Is this something you would be willing to change/implement? Maybe as a boolean/parameter in the options?