Color for debug drawing, packed 0xRRGGBB (b2HexColor). C treats the enum as
a plain integer (shape custom colors are arbitrary u32 values), so the Rust
port is a newtype over u32 with the named palette as associated constants.
Debug drawing callbacks and options (b2DebugDraw). C carries function
pointers plus option fields in one struct initialized by
b2DefaultDebugDraw; the Rust port is a trait where every method has a
default body matching those defaults (draw callbacks default to no-ops so
an implementation can supply only the subset it cares about, options
default to the b2DefaultDebugDraw values). Callbacks receive world
coordinates: in large world mode Pos/WorldTransform translations are
double precision so they stay accurate far from the origin.