Add instrumentation for floating-point exceptions

Description

Trap floating-point exceptions in parts of the code. Example:

Debug = instrument

%InstrumentFunctions
  "electrons/eigensolver.F90.eigensolver_run" | fenv
%

Basically equivalent to recompiling with -ffpe-trap=zero,invalid,overflow,underflow, but switchable at runtime and selective on a per-function basis.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.