legion_prof_rs: Attach deppart channels to each node

This MR restores deppart channels.

Since deppart operaitons have no source or destination memory, I attach them to the node that logged the operation. I'm not sure how correct that is, but it's the best we can do at the moment with the logging information we have.

In the process I decided to rip out the guts of ChanID and replace it with an enum that directly represents the information we have about each channel. So, no more src: Option<MemID>. Now we have Copy { src: MemID, dst: MemID } and so on.

The new UI renders everything correctly. You will now see a deppart channel under each node and the utilization gets summed up along with all the other channels into the per-node and overall channel utilizations correctly.

I hacked the old UI to at least generate per-node deppart files. The JavaScript frontend isn't able to render it and at the moment I don't have the patience to make it do so right now.

I haven't touched Python at all and it will probably cause mismatches in the output.