GitHub Artifacts API update

[mwu-tow]

GitHub recently announced a new version of their Artifacts API (v2) along with updated @actions/upload-artifact action.

The Rust build script has its own implementation of the API, allowing to upload and download artifacts from within the build context. It wasd modeled after the now-outdated @actions/upload-artifact action, and needs to be updated to work with the new API.

The GitHub is going to eventually disable the old API. The old upload-artifact action will be deprecated on June (v3) and November (v4). The Rust implementation should be updated or replaced before that.

The new API has some important benefits, mainly the ability to download artifacts from the run before the workflow completion (without need for internal APIs). If the build script is replaced, this issue is essentialy no-op, as long as the new workflow definitions use the v4+ of the action.