Implement checksum types
To track the various checksums of a package, we need to implement `B2Sum`, `CkSum`, `Sha1Sum`, `Sha224Sum`, `Sha256Sum`, `Sha384Sum`, `Sha512Sum` types (see repod for examples: https://gitlab.archlinux.org/archlinux/repod/-/blob/cc0e43c7c858c679027068639e7db554fb78aa21/repod/files/srcinfo.py)
issue