[R] On-demand serialization + standardization of attributes (#9924)

---------

Co-authored-by: Jiaming Yuan <jm.yuan@outlook.com>

R-package/NAMESPACE

@@ -2,16 +2,19 @@
 
 S3method("[",xgb.DMatrix)
 S3method("dimnames<-",xgb.DMatrix)
+S3method(coef,xgb.Booster)
 S3method(dim,xgb.DMatrix)
 S3method(dimnames,xgb.DMatrix)
+S3method(getinfo,xgb.Booster)
 S3method(getinfo,xgb.DMatrix)
 S3method(predict,xgb.Booster)
-S3method(predict,xgb.Booster.handle)
 S3method(print,xgb.Booster)
 S3method(print,xgb.DMatrix)
 S3method(print,xgb.cv.synchronous)
+S3method(setinfo,xgb.Booster)
 S3method(setinfo,xgb.DMatrix)
 S3method(slice,xgb.DMatrix)
+S3method(variable.names,xgb.Booster)
 export("xgb.attr<-")
 export("xgb.attributes<-")
 export("xgb.config<-")
@@ -26,13 +29,13 @@ export(cb.save.model)
 export(getinfo)
 export(setinfo)
 export(slice)
-export(xgb.Booster.complete)
 export(xgb.DMatrix)
 export(xgb.DMatrix.hasinfo)
 export(xgb.DMatrix.save)
 export(xgb.attr)
 export(xgb.attributes)
 export(xgb.config)
+export(xgb.copy.Booster)
 export(xgb.create.features)
 export(xgb.cv)
 export(xgb.dump)
@@ -41,10 +44,12 @@ export(xgb.get.DMatrix.data)
 export(xgb.get.DMatrix.num.non.missing)
 export(xgb.get.DMatrix.qcut)
 export(xgb.get.config)
+export(xgb.get.num.boosted.rounds)
 export(xgb.ggplot.deepness)
 export(xgb.ggplot.importance)
 export(xgb.ggplot.shap.summary)
 export(xgb.importance)
+export(xgb.is.same.Booster)
 export(xgb.load)
 export(xgb.load.raw)
 export(xgb.model.dt.tree)
@@ -56,10 +61,8 @@ export(xgb.plot.shap.summary)
 export(xgb.plot.tree)
 export(xgb.save)
 export(xgb.save.raw)
-export(xgb.serialize)
 export(xgb.set.config)
 export(xgb.train)
-export(xgb.unserialize)
 export(xgboost)
 import(methods)
 importClassesFrom(Matrix,dgCMatrix)
@@ -88,8 +91,10 @@ importFrom(graphics,title)
 importFrom(jsonlite,fromJSON)
 importFrom(jsonlite,toJSON)
 importFrom(methods,new)
+importFrom(stats,coef)
 importFrom(stats,median)
 importFrom(stats,predict)
+importFrom(stats,variable.names)
 importFrom(utils,head)
 importFrom(utils,object.size)
 importFrom(utils,str)