mlr3 0.21.0

• BREAKING CHANGE: Deprecated data_format and data_formats for Learner, Task, and DataBackend classes.
• feat: The partition() function creates training, test and validation sets now.
• perf: Optimize the runtime of fixing factor levels.
• perf: Optimize the runtime of setting row roles.
• perf: Optimize the runtime of marshalling.
• perf: Optimize the runtime of Task$col_info.
• fix: column info is now checked for compatibility during Learner$predict (#943).
• BREAKING CHANGE: The predict time of the learner now stores the cumulative duration for all predict sets (#992).
• feat: $internal_valid_task can now be set to an integer vector.
• feat: Measures can now have an empty $predict_sets (#1094).
  This is relevant for measures that only extract information from the model of a learner (such as internal validation scores or AIC / BIC)
• BREAKING CHANGE: Deprecated the $divide() method
• fix: Task$cbind() now works with non-standard primary keys for data.frames (#961).
• fix: Triggering of fallback learner now has log-level "info" instead of "debug" (#972).
• feat: Added new measure regr.pinball here and in mlr3measures.
• feat: Added new measure mu_auc here and in mlr3measures.
• feat: Add option to calculate the mean of the true values on the train set in msr("regr.rsq").
• feat: Default fallback learner is set when encapsulation is activated.
• feat: Learners classif.debug and regr.debug have new methods $importance() and $selected_features() for testing, also in downstream packages.
• feat: Create default fallback learner with default_fallback().
• feat: Check column roles when using $set_col_roles() and $col_roles.
• fix: Add predict set to learner hash.
• BREAKING CHANGE: Encapsulation and the fallback learner are now set with the $encapsulate(method, fallback) method.
  The $fallback field is read-only now and the encapsulate status can be retrieved from the $encapsulation field.