Reduce unsafe surface and duplicate wrappers in solverforge-cvrp

[blackopsrepl]

Summary

solverforge-cvrp currently combines repeated unsafe dereferences with duplicate thin wrapper APIs.

Problem

The crate relies on *const ProblemData-style access patterns and exposes overlapping helpers such as assign_route and set_route.

Why This Matters

This raises maintenance cost and safety risk in a public helper API and makes the surface harder to reason about.

Proposed Work

• Consolidate duplicate route helpers.
• Strengthen documentation for safety invariants.
• Investigate safer ownership/reference patterns where feasible.
• Re-evaluate what should be publicly re-exported from the facade crate.

Acceptance Criteria

• Duplicate wrapper surface is reduced.
• Safety invariants are explicit and tested.
• The public API is easier to reason about.

Source

Derived from PR #3 (PRODUCTION_REVIEW_ISSUES_2026-03-20.md).

[blackopsrepl]

Resolved by #21.

We reduced the unsafe surface in solverforge-cvrp by centralizing raw ProblemData pointer access behind narrow helpers, unifying route replacement behind a canonical API, and adding a regression check that rejects missing shared problem data for non-empty fleets.