Changes for new version of xgboost

[topepo]

Closes #28

See dmlc/xgboost#11430

There is no version requirement for xgboost in the description file. Once the new version of xgboost is on CRAN, we can revert c2f87f9 and send xrf to CRAN.

Main changes here:

• xrf requires R >= 4.3 due to xgboost requirement. 😢
• Use xgb.train() instead of xgboost().
• Helper function to populate the xgb arguments.
• Archive of previous fit to verify backwards compatibility for previously fit models.
• Small changes to summary.xrf().

[topepo]

I think XGBoost has sent their new version to CRAN. Would you like me to do anything different for either of these comments?

[holub008]

Thank you for the explanations, we are good! I got the failing build alert from CRAN this afternoon, so let's get it out the door. If you add in the xgb version requirement > 3.1.2.1 and cleanup the dev xgb install, I'll merge this in, do some final testing, and publish to CRAN.

I'm so appreciative of your work @topepo !

[topepo]

I made those updates. Good luck 🤞