add scipy-stubs as non-typeshed stub package (#18832)

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SciPy itself has no `py.typed` and barely any stubs, so I wrote
[`scipy-stubs`](https://github.com/scipy/scipy-stubs). Recently, it has
been accepted as an official scipy project.
This stubs-only package is *complete* (no `untyped`) and *valid*
(according to mypy, stubtest, pyright, basedmypy and basedpyright), and
carefully annotated (by humans).
And for what it's worth, it's also on the list of `mypy_primer`
projects.

I'm open to any feedback, questions, and ideas in general; no need to
hold back :)


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Author: jorenham

mypy/stubinfo.py

@@ -291,6 +291,7 @@ def stub_distribution_name(module: str) -> str | None:
     # for additions here
     "pandas": "pandas-stubs",  # https://github.com/pandas-dev/pandas-stubs
     "lxml": "lxml-stubs",  # https://github.com/lxml/lxml-stubs
+    "scipy": "scipy-stubs",  # https://github.com/scipy/scipy-stubs
 }