Decouple the did:jolo prefix from internal library functions.

[Exulansis]

Description

In order to ensure that the library can support interactions with DIDs anchored on different networks (according to different method specifications), we need to ensure the did:jolo prefix is never explicitly assumed in the inner / helper functions of the library.

Note: This issue was already addressed as part of issue #328 (pr #339) and eventually merged into 4.0-beta1 through #327. In order to simplify the review and feedback process, we decided it can be re-implemented (reusing existing code where possible) as a separate PR.

For reference purposes, please see the issues mentioned above, and this notion document

[Exulansis]

Additional note - #339 also overhauls the integration tests. When re-implementing this should be part of a separate issue, namely #362.