Add libplacebo

[Tobias-Fischer]

Checklist

• Title of this PR is meaningful: e.g. "Adding my_nifty_package", not "updated meta.yaml".
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[github-actions]

Hi! This is the staged-recipes linter and your PR looks excellent! 🚀

[conda-forge-admin]

Hi! This is the friendly automated conda-forge-linting service.

I wanted to let you know that I linted all conda-recipes in your PR (recipes/libplacebo/recipe.yaml) and found some lint.

Here's what I've got...

For recipes/libplacebo/recipe.yaml:

• ❌ If python is a host requirement, it should be a run requirement.

_{This message was generated by GitHub Actions workflow run https://github.com/conda-forge/conda-forge-webservices/actions/runs/12444879720. Examine the logs at this URL for more detail.}

[conda-forge-admin]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipes/libplacebo/recipe.yaml) and found it was in an excellent condition.

[Tobias-Fischer]

@conda-forge/help-c-cpp this is ready for review, many thanks :)