Clarify options2 exercise comments

[wcy6457]

Summary

• Clarify that the first TODO should bind the inner Option value to word with if let.
• Explain what Vec::pop() does and why popping from Vec<Option<i8>> produces nested Option values.
• Add a short description of the intended while let loop behavior.

Testing

• cargo fmt --all --check

I also tried broader local checks, but they were blocked by unrelated/current local issues: cargo dev check --require-solutions stopped on exercises/03_if/if1.rs metadata, and cargo test --workspace on Windows stopped because cmd::tests::test_run_cmd could not find an echo program.

Disclosure

This PR was prepared with assistance from OpenAI Codex.

[senekor]

This PR was prepared with assistance from OpenAI Codex.

Thanks for the heads-up. If it wasn't worth your time to write it, it's not worth our time to read it.