Add multiprocessing.heap submodule (#8412)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

stdlib/multiprocessing/heap.pyi

@@ -0,0 +1,36 @@
+import sys
+from _typeshed import Incomplete
+from collections.abc import Callable
+from mmap import mmap
+from typing import Protocol
+from typing_extensions import TypeAlias
+
+__all__ = ["BufferWrapper"]
+
+class Arena:
+    size: int
+    buffer: mmap
+    if sys.platform == "win32":
+        name: str
+        def __init__(self, size: int) -> None: ...
+    else:
+        fd: int
+        def __init__(self, size: int, fd: int = ...) -> None: ...
+
+_Block: TypeAlias = tuple[Arena, int, int]
+
+if sys.platform != "win32":
+    class _SupportsDetach(Protocol):
+        def detach(self) -> int: ...
+
+    def reduce_arena(a: Arena) -> tuple[Callable[[int, _SupportsDetach], Arena], tuple[int, Incomplete]]: ...
+    def rebuild_arena(size: int, dupfd: _SupportsDetach) -> Arena: ...
+
+class Heap:
+    def __init__(self, size: int = ...) -> None: ...
+    def free(self, block: _Block) -> None: ...
+    def malloc(self, size: int) -> _Block: ...
+
+class BufferWrapper:
+    def __init__(self, size: int) -> None: ...
+    def create_memoryview(self) -> memoryview: ...