Merge Object Histories Across Two Tracking Systems

Implement an `ObjectTracker` that links IDs from tracking systems A and B, accepts observations from either system, and returns the combined chronological history for the underlying real-world object from either ID namespace. Requirements Two independent components, System A and System B, track real-world objects and assign system-local string IDs. The same real object may have different IDs in the two systems. Implement an ObjectTracker with these APIs: addLink(a_id, b_id): declare that an ID from System A and an ID from System B identify the same real object. addObservation(observation): add an observation emitted by either system. getHistory(system, id): query by an ID from either system and return the complete history for that real object. A returned history must include observations from both systems. Sort the result in chronological timestamp order. Preserve each observation's original source system, source ID, and metadata.