Upgrade SymPy Version & Extend CI

• Raise SymPy upper limit to 1.12.1
• Introduce nightly tests against sympy pre-releases

tests/cumulantmethod/test_flow_around_sphere.py

-#%%
 import pytest
 import numpy as np
 from dataclasses import replace
@@ -161,7 +160,3 @@ def test_flow_around_sphere_long(stencil, galilean_correction, fourth_order_corr
     if fourth_order_correction and stencil.Q != 27:
         pytest.skip("Fourth-order correction only defined for D3Q27 stencil.")
     flow_around_sphere(stencil, galilean_correction, fourth_order_correction, 20, 3000)
-
-
-#%%
-test_flow_around_sphere_short(Stencil.D2Q9, False, False)
\ No newline at end of file