Add sing-box

[XhstormR]

Checklist

• Title of this PR is meaningful: e.g. "Adding my_nifty_package", not "updated meta.yaml".
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[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/sing-box/recipe.yaml) and found it was in an excellent condition.

I do have some suggestions for making it better though...

For recipes/sing-box/recipe.yaml:

• ℹ️ License is not an SPDX identifier (or a custom LicenseRef) nor an SPDX license expression.

Documentation on acceptable licenses can be found here.

_{This message was generated by GitHub Actions workflow run https://github.com/conda-forge/conda-forge-webservices/actions/runs/24787049201. 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/sing-box/recipe.yaml) and found it was in an excellent condition.

[XhstormR]

@conda-forge-admin, please rerender

[XhstormR]

@conda-forge-admin, please restart ci

[XhstormR]

@conda-forge/help-go, ready for review!