fix(containers): include infrastructure deps for nested container builds

[domenkozar]

When building a container from within a shell container, the container infrastructure derivations (mkRoot, mkEtc, mkTmp) were not available in the Nix store because they were only used in copyToRoot but not included as layer dependencies.

This fix adds these derivations as deps in a base layer, ensuring they're registered in the Nix database within the container and available when building nested containers.

Fixes #2272

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