Update documentation to avoid filters as flt, aggregations as aggs and spell them out instead

[andeplane]

Describe the bug
In many of the examples in the documentation, we have imports like ... filters as flt. It looks inspired from import matplotlib.pyplot as plt, but doesn't add much value imo, and seems like it might make AI confused in code generation (also me!)

I'd like to update the documentation to import them with filters and aggregations spelled out.

[haakonvt]

@andeplane What about rather always importing them explicitly? I.e. change all to from ... import And, Equals