feat(core): integrate domain + full agent address in Envelope and handler

[Archento]

Proposed Changes

This PR will enable users to set the domain name of an agent they have registered. The domain parameter will be set once the agent has started and successfully verified that the domain actually belongs to this agent.

In subsequent messages the agent will use this domain as well as the prefix when sending messages, i.e. it will be part of the Envelope and available in the message handler through the sender variable.

Types of changes

• [ ] Bug fix (non-breaking change that fixes an issue).
• [x] New feature added (non-breaking change that adds functionality).
• [x] Breaking change (fix or feature that would cause existing functionality to stop working as expected).
• [ ] Documentation update.
• [ ] Something else (e.g., tests, scripts, example, deployment, infrastructure).

Checklist

• [x] I have read the CONTRIBUTING guide
• [x] Checks and tests pass locally

If applicable

• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added/updated the documentation (executed the script in python/scripts/generate_api_docs.py)

Further comments

This needs to be tested for Agentverse compatibility.