Replace data structures lesson with floating point comparisons

[LiamPattinson]

• Don't need to teach so much on lists/dicts. Can mention that these can be tested for equality somewhere earlier, but not dwell on it too much.
• Focus instead on floating point tolerances, as most students will be scientists and this will be a common issue. Start with assert np.isclose(x, y, rtol=rtol, atol=atol).
• Then teach np.testing etc as the preferred solution.

This will prime the students for snaptol in the following lesson.