Apply a camera profile's HueSatMap and LookTable after exposure

The second half of D20: a camera_profile scene operation at order 25
that converts working colour into linear ProPhoto, runs the DNG SDK's
HSV lookup through the HueSatMap and then the LookTable, and converts
back. Hue and saturation do not change under the uniform gains before
it, so a 2.5-D HueSatMap gives the same answer as straight after the
matrix, and the look sees the photographer's exposure as it does in
the SDK. Two departures for scene-referred values: value is not
clamped on the way out, and a colour outside ProPhoto passes through.

The operation holds only the switch (on by default) and a look
strength of 0-200 %. It is composed while the switch is on — a new
Operation::composes() separates "does something" from "moved from the
defaults", so an untouched raw renders through its profile and still
writes nothing. The tables come from the source: dr-gpu uploads the
ones DemosaicedImage carries into a storage buffer at @binding(8),
whose two-entry header tells the fragment whether there is anything to
apply, and binds a header of zeros for every other source.

apply_reference is the lookup on the CPU. The GPU test holds the
shader to it over 256 colours, through synthetic tables strong enough
that a wrong index shows, and through the library's real Adobe
Standard tables when the 6D DNG is present.

docs/dev/requirements.md

@@ -459,7 +459,7 @@ FR-DEV-3j's default, for every body. ΔE2000 validation against ColorChecker ref
 once DCP support lands.
 For item 4: the lookup follows the DNG SDK's on `[0, 1]` and leaves values above 1.0 above it;
 grey and an identity table pass through unchanged; the shader agrees with the CPU reference; with
-the switch off, or no profile, the render is unchanged to the bit (camera-profiles.md §8).
+the switch off the render is to the bit the one with no profile (camera-profiles.md §8).
 
 **FR-DEV-3f — Look emulation.** Support HaldCLUT import, which inherits the existing free film
 simulation ecosystem at near-zero implementation cost, plus reading the in-RAF film simulation tag