DEVX-155: fix: use /dev/shm/docker.sock socket for local dockerd

The existing dockerd holds /var/run/docker.sock and can't be killed
from inside the container (different PID namespace). Use a new socket
path /dev/shm/docker.sock and data root /dev/shm/docker (16G tmpfs).

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

tests/unit/test_start_docker.py

@@ -257,7 +257,7 @@ class TestStartDockerDaemon:
         with patch("builtins.open", mock_open(read_data="dockerd error log")):
             assert start_docker_daemon(timeout=3) is False
         mock_popen.assert_called_once()
-        assert mock_sleep.call_count == 4  # 1 pkill + 3 timeout
+        assert mock_sleep.call_count == 3
 
     @patch("devx.molecule.start_docker.glob.glob", return_value=[])
     @patch("devx.molecule.start_docker._diagnose_socket")
@@ -311,7 +311,7 @@ class TestStartDockerDaemon:
         mock_ready.side_effect = [False, False, True]
         assert start_docker_daemon(timeout=5) is True
         assert mock_popen.call_count == 1
-        assert mock_sleep.call_count == 2  # 1 pkill + 1 timeout
+        assert mock_sleep.call_count == 1
 
     @patch("devx.molecule.start_docker._diagnose_socket")
     @patch("devx.molecule.start_docker._get_docker_free_bytes", return_value=100 * 1024**3)