Ask which frame this was taken on, because grain is enlargement

A crystal is a fixed size in micrometres. How grainy a photograph looks is
therefore not a property of the emulsion alone -- it is film size against
output size, and the frame is the half a digital file cannot supply.

This assumed 35 mm for everything. The same emulsion on 4x5 averages about
3,800 crystals into the pixel that holds 300 on 35 mm, so it renders roughly
3.5 times smoother at the same print; every large-format photograph was being
rendered as grainy as a half-frame.

`Format` now carries the real image widths -- the gate, not the nominal inches,
since a "4x5" exposes about 121 mm -- and the film node asks for it. It is a
genuinely fixed list, unlike the stocks, so it is a declared `enum` parameter
and gets its control, its sidecar entry and its undo step for nothing.

It is also the first enum in the develop chain, and it broke two tests by
being one. A row has to compare equal to itself across two builds or
`sync_rows` replaces it on every parameter event -- destroying the elements
built from it, including whichever TouchArea holds the current gesture, so the
format picker would have fought every slider drag in the panel. `ModelRc`
compares by identity and the row built a fresh choices model each call.

`no_choices` already shares one empty model for exactly this reason, and the
build site already said "see no_choices for why the identity matters". The fix
follows it: memoise the model per variant list. Curve rows solve the same
problem the other way, writing values through the existing model, which is not
needed here -- a variant list is fixed at compile time, so one model can serve
forever.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

core/dr-film/src/lib.rs

@@ -38,6 +38,7 @@
 //! auditable. The sRGB reflectance basis is Mallett & Yuksel (2019).
 
 pub mod bake;
+pub mod boolean_grain;
 mod built_in;
 pub mod grain;
 pub mod profile;
@@ -45,7 +46,8 @@ pub mod spectrum;
 pub mod tables;
 
 pub use bake::{bake, Baked, Recipe};
-pub use grain::Grain;
+pub use boolean_grain::BooleanGrain;
+pub use grain::{Format, Grain};
 pub use profile::{Kind, Profile, Stage, Support};
 
 use built_in::BUILT_IN;