Add Rust dependency analyzer

[tnm]

Summary

• Adds RustDependencyAnalyzer for analyzing Rust crate dependencies
• Parses Cargo.toml for crate metadata and external dependencies
• Extracts use, mod, and extern crate statements via tree-sitter (with regex fallback)
• Classifies imports as internal, std (std, core, alloc, proc_macro, test), or external
• Registered in factory method and CLI (kit dependencies . --language rust)

Test plan

• 17 unit tests covering basic functionality, import types, cycles, exports
• Performance benchmarks added (6.3ms @ 100 modules, on par with Go/Python)
• Lint passes