[Rust][Map] Add safe board and cell-object iteration

[utilForever]

Parent: #137

Goal

Allow callers to inspect dimensions and stacked object records using Rust collections or iterators.

Scope

• Use the C sizing convention safely
• Validate coordinates before or at the FFI boundary
• Avoid borrowed views into mutable native storage unless proven safe

Non-goals

• Mutable editor APIs
• Sprite access
• Zero-copy views without a measured need

Acceptance criteria

• Iteration returns every object exactly once according to the C contract.
• Empty and stacked cells are represented correctly.
• Returned values remain valid independently of later native buffer reuse.

Verification

Compare Rust enumeration with C++ snapshots for empty, stacked, and boundary cases.