[partaevil]

Shared native documentation imports rapier3d and uses 3D/f32-specific constructors in
examples compiled by all four core crates. For example, cargo test -p rapier2d --doc 'data::arena::Arena<T>::contains' fails with E0433 on the base revision.

Use hidden aliases for the selected crate, dimension-independent vector expressions,
explicit 2D/3D constructor branches and math::Real values. Only documentation comments in
22 files change. The 92 executable snippets and 15 existing ignored snippets per variant
are preserved; non-documentation source and ignored blocks are unchanged.

Validation on pinned base 475caa3f: the isolated four-crate native workspace passes 368
doctests with 60 existing ignored snippets in each of the default and parallel matrices.
Those checks were run alongside the separate origin proposal and parallel-test fixture
repair; this PR contains neither. The original pristine-source 2D import failure was
reproduced independently. Representative command for each selected crate:

cargo test -p rapier2d --doc
cargo test -p rapier2d --doc --features parallel

Repeat for rapier3d, rapier2d-f64 and rapier3d-f64. This is documentation portability;
no runtime behavior or example ignore count changes.