Add tests to some of the Rust functions

Description

The following functions still need a unit test:

• send_credential_request
• handle_oid4vp_authorization_request
• handle_siopv2_authorization_request

This needs to test if the connections/credentials are correctly accepted and if the history event is correctly added.

Motivation

We need to better know if we break existing code when we make changes to the code base

Resources

No response

To-do List

• [ ] Add unit tests for send_credential_request
• [ ] Add unit tests for handle_oid4vp_authorization_request
• [ ] Add unit tests for handle_siopv2_authorization_request

Add tests to some of the Rust functions