Read DCP camera profiles: embedded in a DNG, or a .dcp beside the app

The first half of D20. dr-decode now finds a camera profile's HueSatMap
and LookTable in the order camera-profiles.md §4 gives: the profile a
DNG embeds, then a .dcp in the profiles directory whose
UniqueCameraModel names the body, then none. A .dcp brings its own
matrices, since its tables were measured against its forward matrix.

The HueSatMap is blended for the frame's colour temperature with the
same mired weight the matrices use, once per decode, and the result
rides on RawImage as profile_tables beside color_matrix, so every path
that renders a decoded file gets the same profile without a setter to
forget. Nothing applies the tables yet.

A profile whose embed policy allows copying can be written back out as
a .dcp (rawler's TIFF writer with the RC magic patched in), which is how
the library's 6D CR2s will get the Adobe Standard their DNGs carry. The
table type lives in dr-types because decode, pipeline and GPU all need
its layout. Tests read the library's 6D DNG when it is present.

ui/dr-ui/src/decoder_seam.rs

@@ -129,6 +129,7 @@ impl Decoder for Stub {
             },
             samples_per_pixel: 1,
             profile: None,
+            profile_tables: None,
             make: "Stubco".into(),
             model: "Stubco One".into(),
         })

ui/dr-ui/src/develop/render.rs

@@ -1616,6 +1616,7 @@ mod tests {
             color_matrix: None,
             samples_per_pixel: 1,
             profile: None,
+            profile_tables: None,
             make: String::new(),
             model: String::new(),
             crop: dr_decode::CropRect {
@@ -1869,6 +1870,7 @@ mod tests {
             color_matrix: Some([1.6, -0.5, -0.1, -0.2, 1.4, -0.2, 0.0, -0.4, 1.4]),
             samples_per_pixel: 3,
             profile: None,
+            profile_tables: None,
             make: String::new(),
             model: String::new(),
             crop: dr_decode::CropRect {

ui/dr-ui/src/develop/white_balance.rs

@@ -232,6 +232,7 @@ mod tests {
             color_matrix: Some(cam_to_srgb),
             samples_per_pixel: 3,
             profile: None,
+            profile_tables: None,
             make: String::new(),
             model: String::new(),
             crop: dr_decode::CropRect {
@@ -305,6 +306,7 @@ mod tests {
             color_matrix: None,
             samples_per_pixel: 3,
             profile: None,
+            profile_tables: None,
             make: String::new(),
             model: String::new(),
             crop: dr_decode::CropRect {
@@ -357,6 +359,7 @@ mod tests {
             color_matrix: None,
             samples_per_pixel: 3,
             profile: None,
+            profile_tables: None,
             make: String::new(),
             model: String::new(),
             crop: dr_decode::CropRect {