Detection age not updated after merging tracked objects

[nmichlo]

Describe the bug

With re-id enabled, detection age is not updated when objects are merged. It makes sense that detection ages should always be sequential in nature, but after merging tracked objects, the detection age can be arbitrary / is left over from the previous tracked object.

NOTE: the order of detections in the past detections list is also not correctly maintained / merged. It seems like past detections should be kept in-order.

To Reproduce
N/A

Expected behavior

The detection ages should be updated to be relative to the start age of the tracked object that the detections are merged into. I.e. the detection ages should follow on sequentially.

Screenshots or videos
N/A

Environment (please complete the following information):

• OS: [e.g. Ubuntu 20.04]
• Python version: [e.g. 3.9.10]
• Norfair version: [e.g. 1.0.0]

Additional context
N/A