Fix Clippy

Clippy issues are warnings, not errors. Never grep for error when looking for clippy issues.

Step 1: Auto-fix

Run make fix to automatically fix clippy warnings:

make fix

Step 2: Fix remaining warnings manually

Check for remaining warnings that couldn't be auto-fixed:

cargo clippy --tests 2>&1 | grep "^warning:" | sort -u

For each remaining warning, find the exact location and fix it manually.