NumPy 2.0 and SymPy 1.11 are incompatible + other issues

See job #1225967.

Our SymPy version is still fixed to 1.11 (why exactly?), which now causes problems together with NumPy 2.0. The symptom: sympify as implemented in 1.11 does not work on numpy data types anymore.

Solution: Upgrade SymPy. Are there any reasons not to? @holzer

There's also some other, minor issues with NumPy 2.0 that can easily be fixed. Patches coming soon.