Add micromamba as a possible install tool and make it default on macOS and Windows

[jaimergp]

Checklist

• Added a news entry
• Regenerated schema JSON if schema altered (python conda_smithy/schema.py)

Investigating performance improvements triggered by conversation at conda-forge/conda-forge.github.io#2323.

We can use micromamba to save some minutes, specially in Windows. To avoid installing Miniforge if possible, I scripted that too instead of hardcoding the logic in the CI workflow template. This opens the possibility of enabling build-locally.py on Windows, similar to macOS' approach.

Live tests available at conda-forge/dav1d-feedstock#21

[beckermr]

pre-commit.ci autofix

[beckermr]

@conda-forge/core @jaimergp This one appears ready for review! Shall we merge?

[wolfv]

Awesome stuff, really looking forward to shave off these minutes from Windows! :)

[jaimergp]

We might need to change the D:\ stuff on Windows so it's configurable (see #2076 for reference). I was hoping to get that one reviewed/merged, then rebase this one to use the things added there.

[beckermr]

Sounds good. We'll wait then.

[jaimergp]

This is getting quite fast now for Windows, under a minute! conda-forge/dav1d-feedstock#21 (comment)

[beckermr]

Lgtm. Merge when you are ready.

[jaimergp]

The only rough edge here is that this doesn't affect Linux at all due to the Docker images. To benefit from micromamba there we would need to:

• Build and publish micromamba images
• Change the pinnings so the docker_images list refers to micromamba. Or maybe we post-process that by adding a clever mapping (e.g. prefixing everything with micromamba-).

Anyway, this is opt-in for now, so there's little risk.

[jaimergp]

Btw, same PR but for staged-recipes: conda-forge/staged-recipes#27753

[beckermr]

Why not set this as the default?

[jaimergp]

To avoid the inconsistency between Linux and the rest, but in a way it's already inconsistent with Docker. We end up providing the same dependencies in the same base environment so I guess there's no point to be overly cautious. I'll flip the default and document this in the schema. Then folks can chime in if they have any thoughts.

[isuruf]

The logic should be flipped if conda_install_tool != 'micromamba'

[jaimergp]

I'm anticipating that the next install tool is a self-contained environment provider like pixi and not another conda-like client that is first provided by a Miniforge-like installation, that's why I went with "special casing" these two.

[isuruf]

Build and publish micromamba images

We can just put micromamba into the existing images. Won't make a difference