feat: introduce family_spec logic for wafer sensor-count partitioning

src/pygui/backend/wafer/__init__.py

@@ -1,4 +1,5 @@
 # ===== Wafer Sub-package =====
+from pygui.backend.wafer.family_spec import sensor_count_for
 from pygui.backend.wafer.wafer_layouts import available_families, load_layout
 from pygui.backend.wafer.zwafer_models import DataRecord, Sensor, ZWaferData
 from pygui.backend.wafer.zwafer_parser import ZWaferParser
@@ -7,4 +8,5 @@ __all__ = [
     "ZWaferData", "Sensor", "DataRecord",
     "ZWaferParser",
     "load_layout", "available_families",
+    "sensor_count_for",
 ]

src/pygui/backend/wafer/family_spec.py

@@ -0,0 +1,9 @@
+"""Single source of truth for the wafer sensor-count partition."""
+
+
+def sensor_count_for(family_code: str) -> int:
+    """Return the number of valid sensor readings for a wafer family code.
+
+    Returns 80 for the "X" family. Returns 244 for every other family
+    code."""
+    return 80 if family_code == "X" else 244