Add rust_demo Cargo project with unit test

[ARod76]

Summary

Adds rust_demo, a minimal Cargo binary crate used to verify the local Rust toolchain setup.

• Scaffolds the project (Cargo.toml, Cargo.lock, src/main.rs)
• Adds an add(a, b) helper and prints a sample sum from main
• Adds a unit test (test_add)
• Includes a project-local .gitignore (/target)

Test plan

• cargo build — compiles cleanly
• cargo run — prints Hello, world! and 2 + 3 = 5
• cargo test — 1 passed, 0 failed

Warp conversation

Co-Authored-By: Oz oz-agent@warp.dev

[ElliotSlusky]

Thanks for taking the time to put this together, @ARod76. I appreciate the PR.

I'm going to close this one, though. rust_demo is a standalone toolchain-verification scaffold, and OpenJarvis doesn't carry demo or example crates that aren't wired into the project itself, so there isn't really a path to merging it as-is.