Improve slow CI

[tdejager]

Problem description

When working and contributing to pixi the CI can be pretty slow. This is because of a number of factors, but I believe we can do some architectual changes to improve.

My idea is mainly to improve pipelining where a single platform can continue its tests without needing to wait on other platforms, while this does not improve the total pipeline speed it would give quicker feedback for the faster platforms. Currently the tests need to wait on all the platforms to be built for example.

Enable better pipelining:

• Use composite actions for the build tasks. So that these can be re-used.
• Make the integration-tests, wheel-tests, and downstream-tests a composite action as well.
• Write out all the pipelines, instead of using matrices, so that we can depend on specific architectures.
• Make the tests a step that is run after the rust compile (this step enables the actual pipelining)
• Make use of nextest archive so that we skip the test compilation.

Other improvements:

• Cross compile to windows-arm from a larger windows runner
• Cross compile to osx-86 from an ARM runner
• Maybe we can include something like: https://github.com/astral-sh/uv/blob/f679987fe1908c8a815dbcbc6a2a112ae49858ba/.github/workflows/ci.yml#L21C1-L46C33 to detect changes
• Add tag for skipping build and using latest binary, this is useful when wanting to make the integration, wheel or downstream-tests succeed.
• Disable Windows-ARM building on feature branches, we don't run any tests for this target.
• Add dev drive for windows: https://github.com/marketplace/actions/setup-dev-drive#examples

Convert to pytest, similar to wheel tests:

• Running examples
• Integration tests

We can transform these tasks into specific issues when needed.