add support for svamp

[niansong1996]

Add prompt files and preprocessing script for SVAMP.

We should be able to reuse the dataset classes we had for GSM8k.

I've already ran the data generation script on the server, TODOs:

• [x] @niansong1996 : test if the code on some smaller model
• [ ] @yilunzhao : running them on all major models