Enhance backend recovery and diagnostics in installation and tuning scripts

- Improved the `install_swarm_comfy` function to handle empty backend states more effectively, introducing recovery mechanisms and enhanced logging for better visibility.
- Updated the `tune_swarm_perf` function to always sanitize backend FDS corruption, ensuring consistent performance tuning.
- Added new tests to validate the functionality of backend recovery and FDS sanitization, ensuring robustness in backend management.

tests/test_wait_backend_idle.py

@@ -39,6 +39,8 @@ def test_install_swarm_comfy_script_payload():
     assert ".gpu-rent-comfy-installing" in text
     assert "RestartBackends" in text
     assert 'bstat == "errored"' in text
+    assert "sanitize_backends_fds" in text or "recover_empty_backends" in text
+    assert "AddNewBackend" in text
 
 
 def test_wait_backend_idle_fail_fast_on_errored(monkeypatch):