Fix: Wrong fString in Cuda Backend

Due to changing the string formating in pystencils, an error occurred in the CUDA backend, which is fixed by changing back to the classical string formating.

Furthermore, I added a compile instruction to test_fast_approximation to catch the error in the test cases, which was thrown at compile time in the pygrandchem module.

pystencils/backends/cuda_backend.py

@@ -98,7 +98,7 @@ class CudaSympyPrinter(CustomSympyPrinter):
         if isinstance(expr, fast_division):
             return "__fdividef(%s, %s)" % tuple(self._print(a) for a in expr.args)
         elif isinstance(expr, fast_sqrt):
-            return f"__fsqrt_rn({tuple(self._print(a) for a in expr.args)})"
+            return "__fsqrt_rn(%s)" % tuple(self._print(a) for a in expr.args)
         elif isinstance(expr, fast_inv_sqrt):
-            return f"__frsqrt_rn({tuple(self._print(a) for a in expr.args)})"
+            return "__frsqrt_rn(%s)" % tuple(self._print(a) for a in expr.args)
         return super()._print_Function(expr)