Update to sbt 2.0.0 and cross-publish plugin for sbt 1.x and 2.x - #7

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: coursier/cache-action@v6. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/