//! Crystal-optics helpers: crystal-axis tilt/azimuth <-> `Vec3` conversion
//! ([`c_axis`]), crystal-system/optical-character string and index conversions plus
//! custom-`GemMaterial` construction ([`crystal_optics`]), tilt-curve SVG path
//! generation for the performance-graph dialog ([`curve_path`]), and the custom
//! material library's own create/edit/delete callbacks ([`custom_materials`]), and the material
//! editor's physics color mode: its pure state ([`physics_state`]), solver worker
//! ([`physics_solver`]) and Slint glue ([`physics_ui`]), and the editor's Dispersion
//! section (Sellmeier/Cauchy coefficients, readout and curve: [`dispersion_editor`]).
//!
//! Grouped together as the material/crystal-optics domain logic that sits underneath
//! the render/tilt/library UI modules, rather than left as flat top-level `gui` files.