Saving/Loading Lrnr_dbarts does not work

[jeremyrcoyle]

From the help on dbarts::bart:

Saving saveing and loading fitted BART objects for use with predict requires that R's serialization mechanism be able to access the underlying trees, in addition to being fit with keeptrees/keepTrees as TRUE. For memory purposes, the trees are not stored as R objects unless specifically requested. To do this, one must “touch” the sampler's state object before saving, e.g. for a fitted object bartFit, execute invisible(bartFit$fit$state).

[jeremyrcoyle]

I couldn't make this work, even with the extra step. I made an issue on the dbarts repo: https://github.com/vdorie/dbarts/issues/19

I'll complete this once that's resolved