Revert "Removed optika.sensors.AbstractCCD for now."

This reverts commit 0b165f4.

optika/sensors.py

@@ -390,3 +390,27 @@ def quantum_efficiency_effective(
     result = transmissivity * (term_1 + term_2 + term_3)
 
     return result
+
+
+class AbstractImagingSensor(
+    optika.surfaces.AbstractSurface[
+        None,
+        MaterialT,
+        optika.apertures.RectangularAperture,
+        optika.apertures.RectangularAperture,
+        None,
+    ],
+):
+    @property
+    def sag(self) -> None:
+        return None
+
+    @property
+    def rulings(self) -> None:
+        return None
+
+
+class AbstractCCD(
+    AbstractImagingSensor[MaterialT],
+):
+    pass