Add Kademlia stats logging for subspace-networking crates.

[shamil-gadelshin]

This PR periodical adds logging of the Kademlia buckets (total known peer number and number of peers without addresses).

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[nazar-pc]

Do you really need to print it though? I think this should be a metric instead. I hope we can remove handle_periodic_tasks completely at some point and make it reactive instead as it should be.

[shamil-gadelshin]

Do you really need to print it though? I think this should be a metric instead. I hope we can remove handle_periodic_tasks completely at some point and make it reactive instead as it should be.

It's helpful to have this in the log to understand how the process goes. As to metrics, they are also helpful. Let me know what metrics do you lack and we will start accumulating those (with subspace_ prefix). I would do that in a separate PR though.

[nazar-pc]

I mean these parameters should probably be metrics in the first place, same for "Current connections and limits" and they should be updated as changes happen, not once every few seconds.

[nazar-pc]

Okay, I don't this is blocking, let's consider metrics as a future upgrade