[Feature Request] Support .obscpio files

[claudio4]

Hello, I would like to propose adding support for consuming .obscpio files directly as a source input for the cargo_vendoer service.

The primary motivation for this feature is to streamline the workflow when integrating with the obs_scm source service. As obs_scm stores the source code it fetches in the obscpio format.

If the maintainers are open to a PR for this functionality, I would be happy to work on the implementation.