Comprehensions: Generators

Description

Practice generator expressions — comprehensions without the brackets,
passed directly into a reducer that consumes them lazily.

Two patterns to internalize:

1. `func(expr for x in xs if cond)` — pass the gen-exp as a sole
   argument and the parentheses can be elided. Use with sum / any /
   all / max / min.
2. `next((expr for x in xs if cond), default)` — find-first with a
   safe default. The default is critical; without it, an empty match
   raises StopIteration.

Traps worth knowing:
- `all([])` is True (vacuous truth). `any([])` is False.
- `max([])` raises; use `max(..., default=0)`.
- `next(gen)` with no default raises on empty.

Coverage map:
    generator + sum/any/all/max       total_squared, any_negative,
                                      all_positive, max_word_length
    next(gen, default) find-first     first_negative, first_key_with_value

Constraints

- Solve each prompt in a single expression where possible.
- Inputs may be empty; handle the empty case via the reducer's
  default argument or next()'s default — NOT a conditional.
- Don't import anything; everything here is plain builtins.