Refactor GPU environment verification and SSH execution for improved flexibility

- Removed the direct injection of environment variables into the script, preventing issues with `from __future__` imports.
- Updated the `run_python` function to accept an `env` parameter for passing runtime environment variables, enhancing script execution control.
- Adjusted tests to verify the new behavior, ensuring that environment variables are correctly set without modifying the script content.

src/gpu_rent/ready.py

@@ -323,7 +323,6 @@ def verify_gpu_env(
         encoding="utf-8"
     )
     swarm_flag = "1" if want_swarm else "0"
-    prefix = f"import os\nos.environ['GPU_RENT_CHECK_SWARM']={swarm_flag!r}\n"
     log(
         "проверка GPU-стека: nvidia-smi, CUDA"
         + (", torch в Comfy venv" if want_swarm else " (llm-only — без torch)")
@@ -337,10 +336,11 @@ def verify_gpu_env(
             out = run_python(
                 cfg,
                 host,
-                prefix + script,
+                script,
                 remote_path="/tmp/gpu-rent-stack_env_probe.py",
                 timeout=180,
                 log=None,
+                env={"GPU_RENT_CHECK_SWARM": swarm_flag},
             )
         except Exception as exc:
             last = [ServiceCheck("gpu-env", False, str(exc)[:200], "vm")]