refactor: extract find_formula helper, simplify recursive_dep_names, serialize cask installs

- Apply code suggestion: chain .to_set(&:name) on if/else in
  recursive_dep_names instead of repeating it in each branch
- Extract duplicated formulae_by_full_name/formulae_by_name lookup
  into find_formula helper used by formula_dep_names and formula_bottled?
- Serialize cask installs via dedicated mutex to prevent interactive
  sudo Password: prompts from interleaving with parallel output