MAINT: add `import numpy as np`

[mdhaber]

Test automatic addition of import numpy as np to files.

[mdhaber]

@tupui I drafted a program that adds the NumPy imports according to the rules we discussed (I think):

• Only add import numpy as np and import matplotlib.pyplot as plt (no other changes)
• Add them a maximum of once per "Example" section
• Add them to the top of the code block where they are first needed. If both are needed at the top of the same block, the NumPy import goes first.
• Changing existing imports is not in scope (and, of course, don't add a duplicate import)

Just thought I'd let you know so you can create your own branch (and I can review it by comparing against this) or you can review mine however you like.

[tupui]

Nice 👍 thanks Matt. I will wait the next community meeting to officialise the discussion outcome and then start working on this. (I wanted to take a decision already last meeting, but nobody was there so we had to postpone)