pixi build is going to be our source -> package command.

Our current design is tracked in #1654

Main goal

Let users create a conda package from their pixi project.

Key wishes

• No lock-in by build tool, let users define what build tool they want to use.
• Let pixi depend on the built packages as a separate path dependency (workspaces)
• Initial goal is conda packages but the design should not limit to that format.

Before the first release we'll merge into the feature/pixi-build development branch. To allow for non breaking releases while this is being build.