[WIP] Feature/improve fuller

When executing the test, the "optimized" version (using static variables in the function for values that are expensive to calculate, e.g. involving std::cbrt) is surprisingly slower than the version without static variables (with compiler optimizations).

Without compiler optimization, the opposite is true (which would be expected).

Making the variables static constexpr (and adapting the relevant methods involved), makes the "optimized" version as fast as the other one.

How should we deal with this? Might be related to #441 (closed)

Closes #389 (closed)