Add stubs for zstd (#9484)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

stubs/zstd/zstd.pyi

@@ -0,0 +1,15 @@
+from _typeshed import ReadableBuffer
+
+class Error(Exception): ...
+
+def ZSTD_compress(__data: ReadableBuffer, __level: int = ..., __threads: int = ...) -> bytes: ...
+def ZSTD_external() -> int: ...
+def ZSTD_uncompress(__data: ReadableBuffer) -> bytes: ...
+def ZSTD_version() -> str: ...
+def ZSTD_version_number() -> int: ...
+def compress(__data: ReadableBuffer, __level: int = ..., __threads: int = ...) -> bytes: ...
+def decompress(__data: ReadableBuffer) -> bytes: ...
+def dumps(__data: ReadableBuffer, __level: int = ..., __threads: int = ...) -> bytes: ...
+def loads(__data: ReadableBuffer) -> bytes: ...
+def uncompress(__data: ReadableBuffer) -> bytes: ...
+def version() -> str: ...