Painting Variant Sprites

Extended explicit supported versions to include pack format 51 for 25w06a. Other than this, it is identical to the initial release.

I probably won't do this again for further snapshots up to release unless a breaking change comes up, which seems unlikely as of right now. The pack should continue to work in future snapshots up to release otherwise. I will upload an official 1.21.5 version once the drop releases.