Server isolation and detailed errors

Isolated the JsonServer to server.py inside protocols/json

Added specific errors for server startup timeout and server startup
failed

Refactored errors for Core to CoreError generic and refactored
StateError to CoreStateMismatchError derived from CoreError

test/manual/peer.py

@@ -0,0 +1,20 @@
+import asyncio
+
+
+async def main() -> None:
+    reader, writer = await asyncio.open_connection(
+        host="127.0.0.1",
+        port=8765,
+    )
+
+    print("Connected")
+
+    try:
+        await asyncio.sleep(10)
+    finally:
+        writer.close()
+        await writer.wait_closed()
+        print("Disconnected")
+
+
+asyncio.run(main())