Show number of tokens used

Question

`/cost` shows total cost in dollars:

```
> /cost
  ⎿  Total cost:            $0.0975
     Total duration (API):  13.2s
     Total duration (wall): 1m 59.9s
     Total code changes:    0 lines added, 0 lines removed
```

Would be great to see total tokens too, which is helpful for calculating cost on Bedrock or alternate models