Update the xxhash and hashlib stubs (#6031)

* `name`, `block_size`, `digest_size` and `digestsize` attributes of hash objects were made read-only.
* It is now a type-checking error to subclass `xxhash` classes, such as `xxhash.xxh32`. Previously it was an error only at runtime.
* `xxhash` functions now accept strings as input and any object with `__index__()` method for `seed` (instead of requiring an integer). They also fail the type checking if no arguments are given.

stdlib/hashlib.pyi

@@ -1,17 +1,16 @@
 import sys
-from _typeshed import ReadableBuffer
+from _typeshed import ReadableBuffer, Self
 from typing import AbstractSet
 
 class _Hash(object):
-    digest_size: int
-    block_size: int
-
-    # [Python documentation note] Changed in version 3.4: The name attribute has
-    # been present in CPython since its inception, but until Python 3.4 was not
-    # formally specified, so may not exist on some platforms
-    name: str
+    @property
+    def digest_size(self) -> int: ...
+    @property
+    def block_size(self) -> int: ...
+    @property
+    def name(self) -> str: ...
     def __init__(self, data: ReadableBuffer = ...) -> None: ...
-    def copy(self) -> _Hash: ...
+    def copy(self: Self) -> Self: ...
     def digest(self) -> bytes: ...
     def hexdigest(self) -> str: ...
     def update(self, __data: ReadableBuffer) -> None: ...