Adding polylog

[cwangaw]

Describe the current issue
According to Prof. Cotter, it is desired to add more special functions.

Describe the solution you'd like
So, it would be great if we can have the polylog function.

Describe alternatives you've considered
I am currently using the mpmath package

def polylog(s,u):
   '''
      usage: given a function u(x), it returns a function f = polylog(s,u(x)) 
             defined in the same finite element space
   '''
   V = u.function_space()
   eval = [float(np.real(mpmath.polylog(s,float(val)))) for val in u.dat.data[:]]
   f = Function(V)
   f.dat.data[:] = eval

   return f

Additional info
https://firedrakeproject.slack.com/archives/C1Q0Y6H8A/p1742408527898489

[dham]

I think I don't straightforwardly see how we would do this. Assigning to @colinjcotter as he seems to have a plan.