KernelStats doesn't handle CPU hotplug (discontiguous CPUs)

I have a system where CPUs have been hot unplugged:

```
cpu 2074740 293711 234994 2597681757 257 22230 26383 0 0 0
cpu0 14996 1543 5186 5195036 1 63 1986 0 0 0
cpu4 10653 1590 913 5205455 0 57 116 0 0 0
cpu8 22749 1621 923 5193341 0 69 101 0 0 0
cpu12 24716 1511 1236 5191184 1 67 90 0 0 0
```

It looks like we assume CPUs are contiguous, and don't have a way to retrieve the CPU IDs.

Start with the KernelStats entry point that parses the Linux procfs CPU statistics shown in the issue, and trace how CPU records are indexed. Confirm how discontiguous IDs such as 0, 4, 8, and 12 are currently handled. Done means hot-plugged systems are parsed without assuming contiguous CPUs and the CPU IDs can be retrieved.

Written by the indexing model from the issue text.