Reduced calls to solve()

[wleoncio]

Inspired by the conversation started by #17 (comment), I've moved one call of solve() on admm_MADMMplasso() (legacy code) up one loop level. Computation savings aren't huge (5%, see below), but it's something.

MADMMplasso version 0.0.0.9016
Unit: seconds
          expr    min       lq     mean   median       uq      max neval
 MADMMplasso() 82.921 83.98975 89.64103 86.89477 93.31642 108.8523    10

MADMMplasso version 0.0.0.9017
Unit: seconds
          expr      min       lq    mean   median       uq      max neval
 MADMMplasso() 79.06337 80.83594 88.9196 88.10198 94.51792 111.9471    10

To reproduce, use this script, remembering to update the path to the dataset (CRC_data_300.rds).