more naics code expansion

Here are the distinct naics codes of each length in the rcra.hnaics table:

```
length | count
-------+-------
1 | 9
2 | 24
3 | 110
4 | 358
5 | 845
6 | 1188
```

Point is they're pretty sparse (i.e. there are not even close to 10^6 six digit codes) so we could probably just expand all of them.