Add KAKDecompostion pass to optimisation_level=2 after routing (#51)

* add post-routing KAKDecomposition pass to OL=2

* consistent syntax

* fix bad syntax

pytket/extensions/pyquil/backends/forest.py

@@ -46,6 +46,7 @@
     EulerAngleReduction,
     CXMappingPass,
     auto_rebase_pass,
+    KAKDecomposition,
     SequencePass,
     SynthesiseTket,
     DecomposeBoxes,
@@ -165,7 +166,10 @@ def default_compilation_pass(self, optimisation_level: int = 2) -> BasePass:
         )
         passlist.append(NaivePlacementPass(self.backend_info.architecture))  # type: ignore
         if optimisation_level == 2:
-            passlist.append(CliffordSimp(False))
+            # Add some connectivity preserving optimisations after routing.
+            passlist.extend(
+                [KAKDecomposition(allow_swaps=False), CliffordSimp(allow_swaps=False)]
+            )
         if optimisation_level > 0:
             passlist.append(SynthesiseTket())
         passlist.append(self.rebase_pass())