Minor improvements to the itertools recipes

[rhettinger]

• Tighten docstrings and comments
• Improve all_equal() example to not have a four that looked like an eight.
• Replace variable name it with iterator which is clearer.
• Removed early yield-from logic from sieve() because it made the code hard to decipher.
• Replace unique_justseem() with set() in totient(). This is shorter, faster, clearer, and removes a dependency.
• Replace variable name p with prime which is clearer.

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📚 Documentation preview 📚: https://cpython-previews--118563.org.readthedocs.build/

[miss-islington-app]

Thanks @rhettinger for the PR 🌮🎉.. I'm working now to backport this PR to: 3.12.
🐍🍒⛏🤖

[bedevere-app]

GH-118565 is a backport of this pull request to the 3.12 branch.