Module correct 

correct(&mut g) — fix ring closure and orientation in place.

Mirrors boost::geometry::correct from boost/geometry/algorithms/correct.hpp and the closure-fix helper at algorithms/correct_closure.hpp.

Per-kind:

• Ring<P, CW, true> → push closing vertex if missing
• Ring<P, CW, false> → pop closing vertex if duplicated
• exterior ring → reverse so its strategy-level signed area (which already folds the declared PointOrder) is positive — i.e. the stored order matches the declaration, for CW- and CCW-declared rings alike
• Polygon outer → as above; inners → opposite of outer
• MultiPolygon → correct each member

Empty and 1-point rings are left unchanged (silent no-op, matching Boost). Cartesian-only: the orientation test uses the Cartesian shoelace area.

Functions

correct

Fix closure and orientation of g in place.

correct_closure

Fix only ring closure, leaving orientation unchanged.