Move numerical functions to `serac` namespace

These are causing conflicts with other numerical functions and should be guarded by our namespace. We should also evaluate whether they should take `double`'s as arguments.

The issue does not name the files or numerical functions involved. Start by locating the numerical functions that conflict with other functions, then determine the required serac namespace scope and whether their arguments should use double; done means the conflicts are resolved and the argument types have been evaluated.

Written by the indexing model from the issue text.