Add IO times for list schedulers

Added:

• IO times for list schedulers.
• Tests for 100 percent test coverage of schedulers.
• A new example showing custom IO times.

Note that !470 (closed) and !469 (merged) must be merged first since I branched from there.

After that, I can do a rebase if desired.

test/test_sfg_generators.py

@@ -744,7 +744,7 @@ class TestLdltMatrixInverse:
             assert np.isclose(actual_values[i], expected_values[i])
 
     def test_20x20_random_spd(self):
-        N = 30
+        N = 20
 
         sfg = ldlt_matrix_inverse(N=N, is_complex=False)