Anton Core Refactor

[MinuraPunchihewa]

This PR implements the base refactor for the core Anton agent.

The following has been accomplished in this PR:

1. The core sub package for Anton has been introduced. This is where the base logic for Anton to be used across the open-source and enterprise (pro) versions will live.
2. The chat session logic has been decoupled from the loop for running the terminal application.
3. The tool registration logic has been refactored; the core tools scratchpad, memorize and recall are registered as part of the session initialization. Extra tools need to be passed as a separate argument. The tools relevant to the open-source terminal app are registered when initializing the session in the chat loop.
4. The other packages for the other components that make up the core including llm, memory and backends have been introduced, but left empty for now. These will be brought in as separate PRs pointing at this branch.

Based on the gaps identified in the study from @ZoranPandovski, this resolves 1 (needs further investigation), 4 and introduces the skeleton for 2, 3 and 6. 7 requires a little more discovery.