- Added support of `blackbox` likelihoods for `ddm` and `ddm_sdv` models.
- Added support for `full_ddm` models via `blackbox` likelihoods.
- Added the ability to use `hssm.Param` and `hssm.Prior` to specify model parameters.
- Added support for non-parameter fields to be involved in the computation of likelihoods.
- Major refactor of the code to improve readability and maintainability.
- Fixed a bug in model.sample_posterior_predictive().