gh-42765 timeit.Timer Documentation Update

[richardhob]

Update the timeit documentation based on discussion in issue #42765.

Resolve Issue #42765

This issue discusses the documentation for the timeit.Timer class, as well as possible improvements. elibendersky provided a patch to update the documentation, and rurpy improved on this in a post. This merge request implements rurpy's version of the timeit.Timer class documentation with some light edits.

The goal of this documentation change is to better explain how to use timeit.Timer, what the input arguments are, and how the args are use to actually time the execution of the provided snippet.

• Issue: [doc] timeit execution enviroment #42765

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📚 Documentation preview 📚: https://cpython-previews--108744.org.readthedocs.build/