mill 1.0.3

[seroperson]

Hello! Thank you for your plugin! Unfortunately, I can't use it anymore due to outdated mill's version.

Here is what was changed:

• mill 1.0.3
• scalafmt 3.8.3
• Minor build.sc refactoring to match 1.0 changes
• Removed cross-publishing (I'm unsure whether you need it for plugins nowadays, but looks like no)
• .mill-version was removed in favor of YAML header in build.sc
• Added mill wrapper script
• cs in ci script was replaced with mill script
• Call scalafmt via mill
• os.pwd call was replaced with BuildCtx.workspaceRoot in DotEnvModule, as os.pwd now returns some strange paths, something like out/dest. Referencing BuildCtx.workspaceRoot matches better with what sbt-dotenv does.

It also would be nice to have it published to Sonatype Central instead of jitpack .. But it's up to you