typing: have readers/writers inherit from BinaryIO

This gives type checkers more awareness. And it will catch issues
if our classes ever diverge from what the IO interface dictates.

zstandard/__init__.pyi

@@ -5,6 +5,7 @@
 # of the BSD license. See the LICENSE file for details.
 
 from typing import (
+    BinaryIO,
     ByteString,
     Generator,
     IO,
@@ -209,7 +210,7 @@ class ZstdCompressionChunker(object):
     def flush(self): ...
     def finish(self): ...
 
-class ZstdCompressionReader(object):
+class ZstdCompressionReader(BinaryIO):
     def __enter__(self) -> "ZstdCompressionReader": ...
     def __exit__(self, exc_type, exc_value, exc_tb): ...
     def readable(self) -> bool: ...
@@ -234,7 +235,7 @@ class ZstdCompressionReader(object):
     def readinto(self, b) -> int: ...
     def readinto1(self, b) -> int: ...
 
-class ZstdCompressionWriter(object):
+class ZstdCompressionWriter(BinaryIO):
     def __enter__(self) -> "ZstdCompressionWriter": ...
     def __exit__(self, exc_type, exc_value, exc_tb): ...
     def memory_size(self) -> int: ...
@@ -316,7 +317,7 @@ class ZstdDecompressionObj(object):
     def decompress(self, data: ByteString) -> bytes: ...
     def flush(self, length: int = 0): ...
 
-class ZstdDecompressionReader(object):
+class ZstdDecompressionReader(BinaryIO):
     def __enter__(self) -> "ZstdDecompressionReader": ...
     def __exit__(self, exc_type, exc_value, exc_tb): ...
     def readable(self) -> bool: ...
@@ -342,7 +343,7 @@ class ZstdDecompressionReader(object):
     def readinto1(self, b) -> int: ...
     def seek(self, pos: int, whence: int = 0) -> int: ...
 
-class ZstdDecompressionWriter(object):
+class ZstdDecompressionWriter(BinaryIO):
     def __enter__(self) -> "ZstdDecompressionWriter": ...
     def __exit__(self, exc_type, exc_value, exc_tb): ...
     def memory_size(self) -> int: ...