Sync pre-release CPython 3.15 branch from GitHub (2026-05-29)

Summary:
Imported python/cpython `3.15.0b1+` from upstream rev [`2f91315`](https://www.github.com/python/cpython/commit/2f9131575b611dfc749242e8bbc6805bbc14683b) (committed 2026-05-29 21:48:10+00:00).

# Commit Info

- Base: (`3.15.0b1+`) - [`21fa311`](https://www.github.com/python/cpython/commit/21fa311c044704a1638b2ae0dc480fd9f7f68159) (commit date: 2026-05-28 22:57:04+00:00)
- Imported: (`3.15.0b1+`) - [`2f91315`](https://www.github.com/python/cpython/commit/2f9131575b611dfc749242e8bbc6805bbc14683b) (commit date: 2026-05-29 21:48:10+00:00)

# Noteworthy file changes

- Low-signal files (3 added) (NEWS.d, docs, .github)

Complete list of added/removed files: https://www.internalfb.com/intern/everpaste/?color=0&handle=GCC3ZiZMwP2Gu3ADAAZBWWepCDE4br0LAAAz

Differential Revision: D106905296

fbshipit-source-id: ccd516a94b62226f44d1e5f84ca6d91f8349a4c8

Author: generatedunixname1734921407115435

Doc/library/pydoc.rst

@@ -68,6 +68,11 @@ will start a HTTP server on port 1234, allowing you to browse the
 documentation at ``http://localhost:1234/`` in your preferred web browser.
 Specifying ``0`` as the port number will select an arbitrary unused port.
 
+.. warning::
+
+   The :mod:`!pydoc` HTTP server is intended for local use during
+   development and is not suitable for production use.
+
 :program:`python -m pydoc -n <hostname>` will start the server listening at the given
 hostname.  By default the hostname is 'localhost' but if you want the server to
 be reached from other machines, you may want to change the host name that the

Doc/reference/datamodel.rst

@@ -496,7 +496,7 @@ subscript notation ``a[k]`` selects the item indexed by ``k`` from the mapping
 :keyword:`del` statements. The built-in function :func:`len` returns the number
 of items in a mapping.
 
-There is currently a single intrinsic mapping type:
+There are two intrinsic mapping types:
 
 
 Dictionaries
@@ -535,6 +535,20 @@ module.
    an implementation detail at that time rather than a language guarantee.
 
 
+Frozen dictionaries
+^^^^^^^^^^^^^^^^^^^
+
+.. index:: pair: object; frozendict
+
+These represent an immutable dictionary.  They are created by the built-in
+:func:`frozendict` constructor.  A frozendict is :term:`hashable` if all of
+its keys and values are hashable, in which case it can be used as an element
+of a set, or as a key in another mapping.  :class:`!frozendict` is not a
+subclass of :class:`dict`; it inherits directly from :class:`object`.
+
+.. versionadded:: 3.15
+
+
 Callable types
 --------------