Add detector architecture + isotropic detectors

src/pg_rad/inputparser/specs.py

@@ -63,6 +63,13 @@ class RelativePointSourceSpec(SourceSpec):
     z: float
 
 
+@dataclass
+class DetectorSpec:
+    name: str
+    eff: float | None
+    is_isotropic: bool
+
+
 @dataclass
 class SimulationSpec:
     metadata: MetadataSpec
@@ -70,3 +77,4 @@ class SimulationSpec:
     options: SimulationOptionsSpec
     path: PathSpec
     point_sources: list[SourceSpec]
+    detector: DetectorSpec