perf: linear reverse-op construction in diff_dicts/diff_sets - #38

Failed to save: Unable to reserve cache with key setup-uv-2-x86_64-unknown-linux-gnu-ubuntu-24.04-3.12.3-pruned-0a7ab915d9f9ed55307b724740f2a8381103f6166a3db382dd3190d6889a3911, another job may be creating this cache.