feat: make plot writing to file optional in plot_grounding_rates

Make writing plots to file optional in the `plot_grounding_rates`
function by introducing a new parameter to control this behavior. This
allows for flexible usage, including previewing plots without generating
files.

src/spinneret/benchmark.py

@@ -381,7 +381,7 @@ def get_shared_ontology(set1: list, set2: list) -> Union[str, None]:
 
 
 def plot_grounding_rates(
-    grounding_rates: dict, configuration: str, output_file: str
+    grounding_rates: dict, configuration: str, output_file: str = None
 ) -> None:
     """
     Plot the grounding rates of the test data.
@@ -426,7 +426,8 @@ def plot_grounding_rates(
     plt.xticks(rotation=-20)
     plt.legend(title="State")
     plt.tight_layout()
-    plt.savefig(output_file, dpi=300)
+    if output_file:
+        plt.savefig(output_file, dpi=300)
     plt.show()