Automate hierarchical prior R2-D2-M2

From [this](https://arxiv.org/pdf/2208.07132.pdf) paper, how much implementable is R2-D2-M2 prior? (any components that might not work under ODE model)

joint regularization of all regression coefficients in
Bayesian linear multilevel models can be carried out. To do so, we have have proposed
the R2-D2-M2 prior that imposes a prior on the global coefficient of determination R2
and propagates the resulting regularization to the individual regression coefficients via
a Dirichlet Decomposition