Read baseline exposure and profile tone curves; carry the ACR3 curve

The decoding half of camera-profiles.md §11-§12. RawImage gains
baseline_exposure: the file's BaselineExposure plus the chosen
profile's BaselineExposureOffset, as the DNG SDK sums them (+0.25 for
the library's 6D DNGs). A profile copied out of a DNG carries that
DNG's baseline as its offset, so the body's CR2s, which have none,
land at the same total.

ProfileTables gains the profile's ProfileToneCurve, resampled at
decode onto 1025 points with a natural cubic spline; an identity curve
counts as none. dr-types now holds Camera Raw's ACR3 default curve,
RawTherapee's adobe_camera_raw_default_curve copied value for value,
for every raw whose profile has no curve. Nothing renders through
either yet.

core/dr-decode/src/lib.rs

@@ -147,6 +147,12 @@ pub struct RawImage {
     /// renders a decoded file renders it through the same profile without
     /// having to be told — see camera-profiles.md §3.
     pub profile_tables: Option<std::sync::Arc<dr_types::ProfileTables>>,
+    /// TRACES: FR-DEV-3e
+    /// Stops the render adds before anything else: the file's
+    /// `BaselineExposure` plus the profile's `BaselineExposureOffset`
+    /// (camera-profiles.md §11). Applied by the GPU side as a gain on the
+    /// camera matrix; `color_matrix` itself stays the file's.
+    pub baseline_exposure: f32,
     /// The body, as rawler cleans the names: what `Make`/`Model` say, and
     /// what a `.dcp`'s `UniqueCameraModel` is matched against.
     pub make: String,
@@ -602,6 +608,7 @@ fn decode_unguarded(bytes: &[u8]) -> Result<RawImage, DecodeError> {
     let dcp::Resolved {
         profile,
         tables: profile_tables,
+        baseline_exposure,
         ..
     } = dcp::resolve(
         profile,
@@ -700,6 +707,7 @@ fn decode_unguarded(bytes: &[u8]) -> Result<RawImage, DecodeError> {
         samples_per_pixel,
         profile,
         profile_tables,
+        baseline_exposure,
         make: image.camera.clean_make.clone(),
         model: image.camera.clean_model.clone(),
     })