gh-119793: Prefer map(..., strict=True) over starmap/zip in examples

[lgeiger]

This is a docs-only change that updates the examples to use map(..., strict=True) instead of starmap(..., zip(..., strict=True)) which should improve readability.

• Issue: Add a "strict" option for map() #119793

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📚 Documentation preview 📚: https://cpython-previews--126407.org.readthedocs.build/

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[vstinner]

LGTM.

Example:

>>> p=[1,2,3]
>>> q=[4,5,6]
>>> import math
>>> math.sumprod(p, q)
32
>>> import itertools, operator
>>> sum(itertools.starmap(operator.mul, zip(p, q, strict=True)))
32
>>> sum(map(operator.mul, p, q))
32