Add support for platform osx-arm64

[pya]

Modern machines with MacOs come with M[1-5] processors, i.e. the platform is osx-arm64. I added osx-arm64 to tool.pixi.workspace.platforms. The package proj was missing. I added it with Pixi. All tests for the environments py311, py312, py313, and dev run my MacBook Pro M1 Max. The tasks build, install, and lint run as well.

[wpbonelli]

thanks @pya! I'm on M2 so should have had this by now :)

[wpbonelli]

looks like hdf5 is missing on mac. any idea whether it's better to get that thru homebrew or conda? conda for consistency?

[pya]

I always go with conda-forge. I really try to avoid homebrew. It broke my system all too often.

[wpbonelli]

well, I guess the right way to do this is to add pixi config to pyproject.toml as described here, but that is a bit verbose and I'd like to try it separately first. so to get this PR in I will just install hdf5 with brew in CI for now.

[wpbonelli]

@pya do you mind either allowing maintainers to push to your PRs or adding a step to the test CI job before the "Setup pixi" step like

   - name: Install HDF5
     if: runner.os == 'macOS'
     run: brew install hdf5

[pya]

@wpbonelli I couldn't find the button that allows pushing to PRs. So I added the task to CI.