Drop numpy 2.0? #20274

SPEC 0 suggests we should drop numpy 2.0. While awaiting more detailed discussion about how strictly we should follow SPEC 0, maybe good to have some background about the simplifications it allows:

• Minor: remove 10 work-arounds in quantity and masked helpers and 13 in related test routines.
• More major: has a bug in the string implementations that prevents Vectorize string input for Angle and SkyCoord #20236 and other vectorization of coordinates to string formatting (those have fall-back, but it is a good example of being forced to worry about incompatibility with an oldest, no longer support version).