Add support for Rust language parsing

[amaar-mc]

Wit currently supports TypeScript/JavaScript and Python. Rust is widely used in the AI tooling ecosystem.

What needs to happen:

• Add tree-sitter-rust.wasm from tree-sitter-wasms package
• Extend createParserService() to load the Rust grammar
• Add Rust symbol extraction (fn, struct, enum, impl, trait, type)
• Add Rust call edge extraction
• Tests

Same pattern as the existing TypeScript/Python implementation.