Introduces IO abstractions apart from asyncio or those attached to IRawConnection

Also adds `msgio` utilities to mirror the Go implementation

libp2p/io/abc.py

@@ -0,0 +1,34 @@
+from abc import ABC, abstractmethod
+
+
+class Closer(ABC):
+    async def close(self) -> None:
+        ...
+
+
+class Reader(ABC):
+    @abstractmethod
+    async def read(self, n: int = -1) -> bytes:
+        ...
+
+
+class Writer(ABC):
+    @abstractmethod
+    async def write(self, data: bytes) -> int:
+        ...
+
+
+class WriteCloser(Writer, Closer):
+    pass
+
+
+class ReadCloser(Reader, Closer):
+    pass
+
+
+class ReadWriter(Reader, Writer):
+    pass
+
+
+class ReadWriteCloser(Reader, Writer, Closer):
+    pass