TYPING: add stubs for _packer and _unpacker (pandas-dev#28135)

pandas/io/msgpack/_packer.pyi

@@ -0,0 +1,22 @@
+# flake8: noqa
+
+class Packer:
+    def __cinit__(self): ...
+    def __init__(
+        self,
+        default=...,
+        encoding=...,
+        unicode_errors=...,
+        use_single_float=...,
+        autoreset: int = ...,
+        use_bin_type: int = ...,
+    ): ...
+    def __dealloc__(self): ...
+    def _pack(self, o, nest_limit: int = ...) -> int: ...
+    def pack(self, obj): ...
+    def pack_ext_type(self, typecode, data): ...
+    def pack_array_header(self, size): ...
+    def pack_map_header(self, size): ...
+    def pack_map_pairs(self, pairs): ...
+    def reset(self) -> None: ...
+    def bytes(self): ...

pandas/io/msgpack/_unpacker.pyi

@@ -0,0 +1,59 @@
+# flake8: noqa
+
+def unpackb(
+    packed,
+    object_hook=...,
+    list_hook=...,
+    use_list=...,
+    encoding=...,
+    unicode_errors=...,
+    object_pairs_hook=...,
+    ext_hook=...,
+    max_str_len=...,
+    max_bin_len=...,
+    max_array_len=...,
+    max_map_len=...,
+    max_ext_len=...,
+): ...
+def unpack(
+    stream,
+    object_hook=...,
+    list_hook=...,
+    use_list=...,
+    encoding=...,
+    unicode_errors=...,
+    object_pairs_hook=...,
+): ...
+
+class Unpacker:
+    def __cinit__(self): ...
+    def __dealloc__(self): ...
+    def __init__(
+        self,
+        file_like=...,
+        read_size=...,
+        use_list=...,
+        object_hook=...,
+        object_pairs_hook=...,
+        list_hook=...,
+        encoding=...,
+        unicode_errors=...,
+        max_buffer_size: int = ...,
+        ext_hook=...,
+        max_str_len=...,
+        max_bin_len=...,
+        max_array_len=...,
+        max_map_len=...,
+        max_ext_len=...,
+    ): ...
+    def feed(self, next_bytes): ...
+    def append_buffer(self, _buf, _buf_len): ...
+    def read_from_file(self): ...
+    def _unpack(self, execute, write_bytes, iter=...): ...
+    def read_bytes(self, nbytes): ...
+    def unpack(self, write_bytes=...): ...
+    def skip(self, write_bytes=...): ...
+    def read_array_header(self, write_bytes=...): ...
+    def read_map_header(self, write_bytes=...): ...
+    def __iter__(self): ...
+    def __next__(self): ...