Add critical path computation

Closes #94 (closed)

I only have one tests, do I need more?

test/test_sfg.py

@@ -1564,6 +1564,7 @@ class TestSFGErrors:
 class TestCriticalPath:
     def test_single_accumulator(self, sfg_simple_accumulator: SFG):
         sfg_simple_accumulator.set_latency_of_type(Addition.type_name(), 5)
-        sfg_simple_accumulator.inputs[0].latency_offset = 0
-        sfg_simple_accumulator.outputs[0].latency_offset = 0
         assert sfg_simple_accumulator.critical_path() == 5
+
+        sfg_simple_accumulator.set_latency_of_type(Addition.type_name(), 6)
+        assert sfg_simple_accumulator.critical_path() == 6