You are a UX designer. Develop a comprehensive guide explaining when to use low-fidelity vs high-fidelity prototypes. The guide must cover: 1) Definitions of each, 2) Pros and cons of each, 3) When to use low-fi (early ideation, quick feedback), 4) When to use high-fi (usability testing, stakeholder presentation), 5) Fidelity spectrum, 6) Tools for each, 7) Examples, 8) Transitioning from low to high, 9) Testing considerations, 10) Best practices.