Fix CI lint job failures from Ruff rule violations

[Copilot]

The lint GitHub Actions job was failing due to Ruff violations introduced across multiple Python modules (primarily line-length, import-order/placement, and ambiguous-name findings). This PR normalizes those files to satisfy the repository’s enforced Ruff policy without changing runtime behavior.

• Failure surface

  • Address Ruff violations reported in the failing run (E501, I001, E402, E741, plus one test-side unused local).

• Code updates

  • Reflow long literals and command strings (notably puzzle metadata/validator strings) to stay within line-length limits.
  • Correct import ordering and move module imports to top-level where required.
  • Rename ambiguous locals (l-style identifiers) to explicit names for lint compliance.

• Scope characteristics

  • Changes are mechanical/compliance-oriented across touched files; logic and interfaces remain unchanged.

# before
def key(l):
    return (
        l.get("id") in solved,
        difficulty_key(l.get("difficulty")),
    )

# after
def key(level):
    return (
        level.get("id") in solved,
        difficulty_key(level.get("difficulty")),
    )