Use Literal type in io and _compression (#6917)

Author: sobolevn

stdlib/_compression.pyi

@@ -1,8 +1,8 @@
 from _typeshed import WriteableBuffer
-from io import BufferedIOBase, RawIOBase
+from io import DEFAULT_BUFFER_SIZE, BufferedIOBase, RawIOBase
 from typing import Any, Callable, Protocol
 
-BUFFER_SIZE: Any
+BUFFER_SIZE = DEFAULT_BUFFER_SIZE
 
 class _Reader(Protocol):
     def read(self, __n: int) -> bytes: ...

stdlib/io.pyi

@@ -5,12 +5,13 @@ from _typeshed import ReadableBuffer, Self, StrOrBytesPath, WriteableBuffer
 from os import _Opener
 from types import TracebackType
 from typing import IO, Any, BinaryIO, Callable, Iterable, Iterator, TextIO
+from typing_extensions import Literal
 
-DEFAULT_BUFFER_SIZE: int
+DEFAULT_BUFFER_SIZE: Literal[8192]
 
-SEEK_SET: int
-SEEK_CUR: int
-SEEK_END: int
+SEEK_SET: Literal[0]
+SEEK_CUR: Literal[1]
+SEEK_END: Literal[2]
 
 open = builtins.open