Add Distribution Name to the `to_dict` Return of Univariate Distributions

[pvk-developer]

Description:

Currently, the Univariate distributions return a dictionary that includes the type of the distribution, represented as the fully qualified Python name (e.g., copulas.univariate.BetaUnivariate).

To improve clarity and usability, it would be helpful to include the native distribution name from SciPy. For example, instead of returning copulas.univariate.BetaUnivariate under the type key, the dictionary should also contain a distribution_name key with the corresponding SciPy distribution name (e.g., beta for the BetaUnivariate distribution). This attribute can be obtained from the instance.MODEL_CLASS.name.