Huge numeric discrepancy introduced by Apple's Rapid Security Response macOS 13.3.1 (a)

Numeric outcomes changed by as much as 3e-3 in Suite.MagneticSpheres.

We should investigate this to find either a newly introduced bug in MacOS, or (far more likely) a numeric instability of our code.

Also submitted at https://discussions.apple.com/thread/254868240, then https://discussions.apple.com/thread/254880143.

First thing to do: upgrade to 13.4 (#602 (closed)).