Improve quiz variety: add multiple question types

[travisjneuman]

Description

Currently all quizzes use multiple-choice format. Add variety by supporting fill-in-the-blank, true/false, and code-completion question types.

Scope

• Update concepts/quizzes/_quiz_helpers.py to support new question types
• Add 2-3 new question types to at least 5 existing quizzes
• Keep the terminal-based interface simple and accessible

Acceptance Criteria

• Quiz helper supports at least 3 question types (multiple choice, true/false, code completion)
• At least 5 quizzes have mixed question types
• All quizzes still run from the terminal with python quiz-name.py
• Scoring works correctly for all question types

[travisjneuman]

Resolved in 36dceb1: Added true/false and code-completion question types to quiz system via ask_true_false() and ask_code_completion() in _quiz_helpers.py. Updated 5 quizzes with mixed question types.