docs: update PEP 561 packaging guidance for setuptools default type info

[daksh1403]

What this PR does
Updates documentation to reflect that setuptools (>=69.0.0)
includes type information by default, clarifies that this behavior
is experimental, and recommends pyproject.toml for new projects.

Scope
Documentation-only change.

Fixes #16551

[wyattscarpenter]

You spuriously include a lot of changes here that aren't related to this PR and in fact are from previous PRs you've submitted here recently.

[wyattscarpenter]

In general it seems like you're submitting a number of PRs to Mypy using an LLM without really understanding what you're doing.

[daksh1403]

Thanks for pointing this out you’re absolutely right.
This PR unintentionally includes changes from several earlier branches I’ve been working on, and it should have been limited strictly to the documentation updates for #16551. That’s my mistake.
I’m going to close this PR and re-submit a clean one with only the minimal, relevant changes for the setuptools type-info documentation update.
Apologies for the noise, and thanks for calling it out.