Drop support for older draft versions

[TimoGlastra]

Now that OID4VCI 1.0 and OpenID4VP 1.0 are both released and supported by this library, we'd like to work towards dropping support for pre-1.0 versions in this library. There's a lot of glue and overly complex code to handle all the drafts. this was great when we didn't have a stable version, but now it just adds complexity, and means we can't efficiently enforce all rules from OpenID4VCI and OpenID4VP 1.0.

My idea was to release 0.3.0 soon (#20) with support for 1.0 and the older drafts. That will provide a good foundation for implementations that need to support multiple versions. And then we can work on the new 0.4.x release in the main branch that doesn't support older drafts.

If you're using this library and have a requirement for pre 1.0 support to be maintained, please comment on this issue, so we know the impact of removing support for older versions.

[hacdias]

I agree with releasing 0.3.0 with support for 1.0 and older drafts. Once we drop support for the older drafts, I'd release 1.0. This way, we can still iron out some potential bugs until 1.0 and we make sure that the first stable release supports the drafts as-is without support for already deprecated things.