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)