LMP pickles were compressed with bzip2, named .gz

Shim in place for a pandas-2.x upgrade, but this shouldn't be necessary.

```
file data/lmps_data_visualization/t7k_v0.4.0-a2_rsvf-20/*.p.gz | awk -F': ' '{print $2}' | uniq
bzip2 compressed data, block size = 900k
```