Merge pull request #301 from anevolbap/issue_300-round_to-optional

Fix #300: Set `round_to` as an optional argument.

causalpy/pymc_experiments.py

@@ -903,7 +903,7 @@ def plot(self, round_to=None):
         )
         return fig, ax
 
-    def summary(self, round_to: None) -> None:
+    def summary(self, round_to=None) -> None:
         """
         Print text output summarising the results