Speed up the cf tactics

This issue is about reviewing the implementation of the tactics in `characteristic` and taking any quick wins on efficiency. A good benchmark would be `examples/pseudo_bool/array`.

Start by locating the tactic implementation in `characteristic` and run or inspect the benchmark at `examples/pseudo_bool/array`. Determine which efficiency improvements are feasible without changing the tactic's behavior, then use that benchmark to confirm a measurable speedup and ensure the existing behavior remains intact.

Written by the indexing model from the issue text.