maths/radix2_fft.py: Fix calculation for Python 3.14

As suggested at:
* #12729 (comment)
* #12710 (comment)

@MaximSmolskiy @KirilBangachev @skirpichev Careful review, please.  I am just implementing the suggestion, but I do not have any expertise in this area.

Author: cclauss

maths/radix2_fft.py

@@ -147,7 +147,7 @@ def __multiply(self):
             inverce_c = new_inverse_c
             next_ncol *= 2
         # Unpack
-        inverce_c = [round(x[0].real, 8) + round(x[0].imag, 8) * 1j for x in inverce_c]
+        inverce_c = [complex(round(x[0].real, 8), round(x[0].imag, 8)) for x in inverce_c]
 
         # Remove leading 0's
         while inverce_c[-1] == 0: