Copy over CG-CLEAN method from ARDG-LibRA to CASA Method is described in detail in: https://ui.adsabs.harvard.edu/abs/2026A%26A...706A...77M/abstract (Mueller, Genie, Bhatnagar 2026: Accelerating the CLEAN algorithm of radio interferometry with convex optimization) For now, only the CG option is implemented, with momentum acceleration to follow later. Implementation is done by adding a new keyword to tclean (majorcycle) detailing which major loop heuristics is used, i.e. CS (Cotton-Schwab) or CG (conjugate gradients) The algorithm and its improvements are tested for continuum, polarization and cube imaging, with a variety of gridders including mosaics,w/a/aw-projection, TBD: validation for mvc A shallow set of examples to reproduce the improvements is linked to the Jira ticket
