V-L3-B2: remove blanket #![allow(...)] in src/main.rs

[hyperpolymath]

Context

Same situation as V-L3-B1 but in src/main.rs, which carries the identical allow block. Sister issue; handle alongside.

What to do

Remove the blanket #![allow(...)] block from src/main.rs. Fix lints at site. Verify with cargo clippy --all-targets -- -D warnings.

Acceptance

• #![allow(...)] block removed from src/main.rs
• cargo clippy --all-targets -- -D warnings is clean