Find hot photosites without repairing them, and measure a sensor's aging

The hot-pixel pass could only repair: it returned how many photosites it
changed and threw away which. find_hot_pixels runs the same pass and
returns them as sensor coordinates, leaving the frame alone, so a sensor's
defects can be tracked across frames.

sensor_scan prints each frame's candidates, and with --probe reads a list
of coordinates back out of every frame. Run over 53 6D raws from 2015 to
2026, it found 32 persistent defects, 2 in 2015 and 32 by 2026, and showed
what a defect map has to account for: a frame that does not flag a
photosite proves nothing unless its neighbourhood is dark, and the 6D
hides some of its defects itself above ISO 5000. docs/dev/sensor-health.md
records the findings and the design they argue for.

core/dr-gpu/tests/hot_pixels.rs

@@ -7,7 +7,7 @@
 //! see of a defect it missed is the coloured cross the demosaic makes of it.
 
 use dr_decode::{CfaPattern, CropRect, RawImage};
-use dr_gpu::{AdjustPass, Demosaicer, GpuContext};
+use dr_gpu::{AdjustPass, Demosaicer, GpuContext, Photosite};
 use dr_pipeline::EditGraph;
 
 const SIZE: u32 = 36;
@@ -171,3 +171,43 @@ fn the_repaired_mosaic_reads_back_with_only_the_defect_changed() {
     let others = (0..raw.data.len()).filter(|&i| i != at);
     assert!(others.into_iter().all(|i| raw.data[i] == before.data[i]));
 }
+
+/// Finding without repairing (docs/dev/sensor-health.md): the same verdict as
+/// the repair, as sensor coordinates, with the frame left as it was. The
+/// sensor health record builds on this, so it must name exactly the
+/// photosites the repair would change — the hot one and the dead one, and
+/// not the star.
+#[test]
+fn finding_names_what_the_repair_would_change_and_changes_nothing() {
+    let Some(ctx) = ctx() else {
+        eprintln!("no GPU adapter; skipping");
+        return;
+    };
+    let d = Demosaicer::new(&ctx).expect("demosaicer");
+    let mut set = vec![(MIDDLE, MIDDLE, WHITE), (9, 25, 0)];
+    for dy in 0..3 {
+        for dx in 0..3 {
+            set.push((4 + dx, 4 + dy, WHITE));
+        }
+    }
+    let raw = frame(CfaPattern::Rggb, 1600, &set);
+    let mut found = d.find_hot_pixels(&raw).expect("find");
+    found.sort_by_key(|p| (p.y, p.x));
+    assert_eq!(
+        found,
+        vec![
+            Photosite {
+                x: MIDDLE,
+                y: MIDDLE,
+                hot: true
+            },
+            Photosite {
+                x: 9,
+                y: 25,
+                hot: false
+            },
+        ]
+    );
+    let mut repaired = raw.clone();
+    assert_eq!(d.repair_hot_pixels(&mut repaired).expect("repair"), 2);
+}