Add Python 3.15 builtins updates

[JelleZijlstra]

Summary

• Add Python 3.15 builtins updates for frozendict, sentinel, lazy imports, generic slice, and bytearray.take_bytes.
• Update directly related frozendict support in collections/opcode.
• Remove corresponding 3.15 stubtest allowlist entries.

Relevant report entries

• Added builtins.frozendict and allowed it in str.maketrans, eval, and exec globals (CPython PR: PEP 814: Add built-in frozendict type cpython#141510; source: https://github.com/python/cpython/blob/main/Objects/dictobject.c)
• Added builtins.sentinel (CPython PR: Implement PEP 661 Sentinel Values cpython#148829; source: https://github.com/python/cpython/blob/main/Objects/sentinelobject.c)
• Added bytearray.take_bytes (CPython PR: Add .take_bytes([n]) a zero-copy path from bytearray to bytes cpython#139871; source: https://github.com/python/cpython/blob/main/Objects/bytearrayobject.c)
• Added support for generic slice (already present upstream; CPython PR: Make slice generic cpython#128335; source: https://github.com/python/cpython/blob/main/Objects/sliceobject.c)
• Added builtins.ImportCycleError and builtins.__lazy_import__ for lazy imports (CPython source: https://github.com/python/cpython/blob/e81025e6d2e01e38c5a5b656af5739ac9df5ff55/Python/bltinmodule.c)
• Changed opcode.opmap to frozendict and added pathlib.PurePath.__vfspath__() for Python 3.15 (CPython sources: https://github.com/python/cpython/blob/e81025e6d2e01e38c5a5b656af5739ac9df5ff55/Lib/opcode.py, https://github.com/python/cpython/blob/e81025e6d2e01e38c5a5b656af5739ac9df5ff55/Lib/pathlib/__init__.py)

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

pandas (https://github.com/pandas-dev/pandas)
- pandas/core/computation/ops.py:328: error: Need type annotation for "_binary_ops_dict" (hint: "_binary_ops_dict: dict[<type>, <type>] = ...")  [var-annotated]

[AlexWaygood]

it seems like the runtime error message if you provide a non-(frozen)dict Mapping is now inaccurate:

>>> str.maketrans(types.MappingProxyType({42: 'foo'}))
Traceback (most recent call last):
  File "<python-input-13>", line 1, in <module>
    str.maketrans(types.MappingProxyType({42: 'foo'}))
    ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: if you give only one argument to maketrans it must be a dict
>>> # au contraire...
>>> str.maketrans(frozendict({42: 'foo'}))
{42: 'foo'}

[AlexWaygood]

An instance of the subclass is returned if you subclass frozendict:

>>> class Foo(frozendict): ...
...
>>> Foo()
Foo()
>>> type(_)
<class '__main__.Foo'>

But these __new__ overloads mean that ty and pyrefly will infer Foo() as resolving to frozendict[Any, Any], which is unfortunate. (Those were the only type checkers I checked other than mypy, which infers Foo for Foo().)

I wondered if you could do this, but mypy has lots of (I think legitimate) complaints about that, so I don't think it's really an option:

Suggested change

	@overload
	def __new__(cls, /) -> frozendict[Any, Any]: ...
	@overload
	def __new__(cls: type[frozendict[str, _VT]], /, **kwargs: _VT) -> frozendict[str, _VT]: ...
	@overload
	def __new__(cls, map: SupportsKeysAndGetItem[_KT, _VT], /) -> frozendict[_KT, _VT]: ...
	@overload
	def __new__(
	cls: type[frozendict[str, _VT]], map: SupportsKeysAndGetItem[str, _VT], /, **kwargs: _VT
	) -> frozendict[str, _VT]: ...
	@overload
	def __new__(cls, iterable: Iterable[tuple[_KT, _VT]], /) -> frozendict[_KT, _VT]: ...
	@overload
	def __new__(
	cls: type[frozendict[str, _VT]], iterable: Iterable[tuple[str, _VT]], /, **kwargs: _VT
	) -> frozendict[str, _VT]: ...
	@overload
	def __new__(cls, /) -> Self: ...
	@overload
	def __new__(cls: type[frozendict[str, _VT]], /, **kwargs: _VT) -> Self: ...
	@overload
	def __new__(cls, map: SupportsKeysAndGetItem[_KT, _VT], /) -> Self: ...
	@overload
	def __new__(
	cls: type[frozendict[str, _VT]], map: SupportsKeysAndGetItem[str, _VT], /, **kwargs: _VT
	) -> Self: ...
	@overload
	def __new__(cls, iterable: Iterable[tuple[_KT, _VT]], /) -> Self: ...
	@overload
	def __new__(
	cls: type[frozendict[str, _VT]], iterable: Iterable[tuple[str, _VT]], /, **kwargs: _VT
	) -> Self: ...

[JelleZijlstra]

Another option is to lie and implement this in __init__ instead, matching __dict__, but that would be inaccurate to the runtime since frozendict constructs itself purely in __new__.

[AlexWaygood]

These are both read-only at runtime -- couldn't we make these @propertys to reflect that?

>>> X = sentinel("X")
>>> X.__name__ = 'Y'
Traceback (most recent call last):
  File "<python-input-2>", line 1, in <module>
    X.__name__ = 'Y'
    ^^^^^^^^^^
AttributeError: readonly attribute
>>> X.__module__ = 'foo'
Traceback (most recent call last):
  File "<python-input-4>", line 1, in <module>
    X.__module__ = 'foo'
    ^^^^^^^^^^^^
AttributeError: readonly attribute

Though I know we're thinking of changing that for __module__.

[AlexWaygood]

Self is accurate here, but since sentinel is @final I feel like we might as well just return sentinel directly? It saves a bit of work for type checkers

Suggested change

	def __new__(cls, name: str, /) -> Self: ...
	def __copy__(self, /) -> Self: ...
	def __deepcopy__(self, memo: Any, /) -> Self: ...
	def __new__(cls, name: str, /) -> sentinel: ...
	def __copy__(self, /) -> sentinel: ...
	def __deepcopy__(self, memo: Any, /) -> sentinel: ...