Test token investigation

[mjuchli-da]

In addition to reviewing #1622.

Research to be conducted by @mateuszpiatkowski-da regarding reference test token project:

• Makes a clear plan based on the PR from Jarek
• How to approach the test-token code and how it should evolve
• Either within the wallet repo or possibly a different repo
• Focuses on separation of concerns and interoperability

[meiersi-da]

Feel free to reach out to me to brainstorm some early ideas and/or validate the chosen approach. I've written two full implementations of test tokens as part of the token standard v2 work, and it would be great if that work could be reused. What's missing from these implementations are the HTTP backends to use them.

The implementations can be found here: https://github.com/canton-network/splice/tree/token-standard-v2-upcoming/token-standard/examples

• splice-test-token-v1 is a V1-only token
• splice-test-token-v2 is a V1/V2 dual version token with multiple authorization models for accounts (e.g., owner-controlled vs. joint-control with a custodian)