Read imports and exports for Rust #41

Context

Hidden coupling (#17) and module depth (#18) read imports and exports through one adapter per language; only TypeScript/JavaScript has one. Rust's module system (mod declarations, mod.rs or name.rs files, use crate::…, pub use re-exports, Cargo workspaces) maps code to files unambiguously and fits module depth particularly well.

Goal

Rust repositories get Coupling.imports and Module.depth like TypeScript repositories do.

Acceptance criteria

• A Rust adapter resolves mod declarations, use crate::, use super::, use self::, and use <workspace crate>:: (crate names from Cargo workspace members) to universe files; external crates are ignored.
• It lists a crate's public surface for depth: pub items reachable from lib.rs, following pub use re-exports; pub(crate) and pub(super) are not public.
• A fixture workspace with two crates, an imported pair, a hidden pair, and a pub use re-export proves both.

References

• Part of Read imports and exports beyond TypeScript and JavaScript #38. Builds on Flag hidden coupling: files that change together without importing each other #17 and Measure module depth as implementation size per exported symbol #18.