Implement order manager

[sauk2]

Summary

Implement OrderManager with pure order lifecycle logic focusing entirely on receiving new orders, validating updates, producing the next graph element and using the graph validator. It must not update robot state and must not depend on StateManager. Related to the work done in #3

• Implement the OrderManager using hard types introduced in PR feat(types): create C++ structs for VDA5050 2.0.0 spec #6
• Accept a const reference to State but treat it as read-only while updating the order
• Make sure there is no interaction with state logic
• Add unit tests