20240417 uri, base58 encoding, padding short names

[benjaminbollen]

fixes #143

• simplify the CIDv0 storage for IPFS metadata to a cleaner storage of sha256 digest of metadata; leaving the IPFS hosting to architecture layer
• basic coverage of unit tests of implemented base58 encoding (used for short and long names in NameRegistry)
• always have short names be padded to 12 characters (it is unlikely an address would result in a shorter short name), so that there is no visual confusion about length of short names