Implement cran loader with package manager mechanism

The extrinsic metadata are provided by the lister as the loading task parameters.

The intrinsic metadata lies within the DESCRIPTION file at the root tree of a tarball [1].

DESCRIPTION uses a simple file format called DCF, the Debian control format.

See [2] for the necessary parsing tools.

• [1] https://r-pkgs.org/description.html

• [2] python3-debian

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Migrated from T2026 (view on Phabricator)