Sync python-mutable-immutable with the updated tutorial

[realpython-bot]

Maintenance sync for Python's Mutable vs Immutable Types: What's the Difference?.

What changed

• point.py: the Coordinate.__set__() descriptor now quotes the attribute name in its error message (can't set attribute 'x'), matching the article's code block and the REPL output it shows.

The rest of the folder already matches the article. This cycle's article edits (Python 3.14 output drift: 15 / 3 → 5.0, the extended __slots__ AttributeError message, the 3.14 unhashable-key message, __static_attributes__ in the class __dict__) only touch REPL output, so none of them need code changes here.

Links

• Draft update (admin): https://realpython.com/pbjt/blog/post/2439/change/
• Maintenance card: https://trello.com/c/D07kvWKp

Verification

• Ran every script on Python 3.14.6, and exercised Point/Immutable in a REPL: can't set attribute 'x', can't set attribute 'unit'.
• uvx ruff@0.14.1 format --check and uvx ruff@0.14.1 check: both pass.

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