update isotope lookup to tabular format. Add primary gamma energy to results plotting

src/pg_rad/simulator/engine.py

@@ -62,6 +62,7 @@ class SimulationEngine:
                 SourceOutput(
                     s.name,
                     s.isotope.name,
+                    s.isotope.E,
                     s.activity,
                     s.pos,
                     dist_to_path)

src/pg_rad/simulator/outputs.py

@@ -13,6 +13,7 @@ class CountRateOutput:
 class SourceOutput:
     name: str
     isotope: str
+    primary_gamma: float
     activity: float
     position: Tuple[float, float, float]
     dist_from_path: float