[Rust][Crates] Define sys and safe-wrapper crate boundaries

[utilForever]

Parent: #137

Goal

Use one low-level FFI crate and one small safe wrapper without adding speculative framework layers.

Scope

• Define workspace or package layout compatible with the repository
• Keep raw declarations isolated from safe ownership APIs
• Document supported Rust and native build expectations

Non-goals

• A crate per C API module
• A Rust simulator reimplementation
• RL-framework-specific crates

Acceptance criteria

• Unsafe declarations are confined to the sys boundary.
• The safe crate can evolve internally without exposing raw handles.
• The layout has one documented build and test path.

Verification

Build empty linked crate targets and review their public dependency direction.