Enable timeline visualizations of object transfers.

[robertnishihara]

It looks something like this. Each "process" refers to an object manager. Black boxes refer to sends and gray boxes refer to receives. Each object has its own color.

In this workload, the bottom node broadcasts 4 objects to 3 other nodes.

All of the little pieces are due to object chunking.

[pcmoritz]

remove this or make it a todo

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