Add premade action models

Basic models:
- [ ] Gaussian random
- [ ] Categorical random
- [ ] Gaussian random walk

Iowa Gambling Task:
- [ ] PVL-Delta
- [ ] ORL

Models from HBayesDM:

The issue body lists three basic models, three Iowa Gambling Task models, and additional models from HBayesDM, but names no files, tests, or model specifications. Start by identifying the package entry points and the expected definitions for each checklist item; done means the requested premade action models are implemented and covered by the project's existing validation or test process.

Written by the indexing model from the issue text.