Hard split of the different OID4VC crates

[nanderstabel]

Description

Specifically the SIOPv2, OID4VC and OID4VCI crates need to be properly split. All common/shared code should be migrated to a new crate: oid4vc-core or oid4vc-common.

Whenever SIOPv2 or OID4VC should be used in unison, their respective feature flags should be used.

Motivation

This is necessary in order for SIOPv2 to be used with and without OID4VP and vice versa.

Resources

No response

To-do List

• Create a new crate and migrate all shared code there.
• feat: add Extension trait for SIOPv2 and OID4VP #60
• Implement feature flags so that SIOPv2 and OID4VP can be used in unison
• Add an integration test to test the implicit flow for siopv2+oid4vp