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/test_core.py

@@ -0,0 +1,18 @@
+import pytest
+from dynalab_core import Core
+from dynalab_core.config import CoreConfig
+from dynalab_core.errors import CoreStateMismatchError
+from test.common import find_available_port
+
+
+def test_core_cannot_start_twice() -> None:
+    port = find_available_port(8765)
+    core = Core(CoreConfig(port=port))
+
+    core.start()
+
+    try:
+        with pytest.raises(CoreStateMismatchError):
+            core.start()
+    finally:
+        core.stop()