fix(hardening): address all PR #157 review findings

Critical:
  - _load_module(): wrap exec_module() in try/except, pop from sys.modules
    on failure so broken modules aren't cached
  - get_comfyui_path(): add _is_comfyui_directory() check to third (CWD walk)
    strategy so a non-ComfyUI directory named "ComfyUI" isn't accepted
  - get_node_class_mappings(): return cached sys.modules["nodes"] if already
    loaded to avoid re-executing nodes.py and losing init_extra_nodes() state

Suggestions:
  - import_custom_nodes(): wrap sys.path filtering in try/finally so path is
    always restored even if _load_module("server") raises mid-execution
  - render.py: auto-discover helpers from generated_helpers.__all__ instead of
    a manually maintained list
  - pyproject.toml: remove duplicate ruff dev dependency (kept standard
    [project.optional-dependencies] form)

Nitpicks:
  - Remove dead imports (types, StringIO) from test_import_path_resolution.py
  - Trim trailing blank lines in pyproject.toml
  - Tone down _load_module docstring: "eliminates ALL" -> "significantly reduces"

Tests (7 new cases):
  - TestLoadModuleFailureCleanup: broken module removed on exec failure, retry
    starts fresh
  - TestLoadModuleTemp: temp modules purged from sys.modules (success + failure)
  - TestRepeatedNodeLoad: repeated _load_module("nodes") returns cached copy
  - TestGetComfyuiPathThirdStrategy: fake "ComfyUI" dir rejected
  - TestImportCustomNodesSysPathRestoration: sys.path restored after crash

comfyui_to_python/generator/render.py

@@ -5,19 +5,7 @@ from typing import Any
 import black
 
 from ..node_runtime import import_custom_nodes
-from .generated_helpers import (
-    _find_from_extension_location,
-    _is_comfyui_directory,
-    _load_module,
-    _load_module_temp,
-    add_comfyui_directory_to_sys_path,
-    add_extra_model_paths,
-    bootstrap_comfyui_runtime,
-    cleanup_comfyui_runtime,
-    find_path,
-    get_comfyui_path,
-    get_value_at_index,
-)
+from . import generated_helpers
 from .model import GenerationPlan
 
 
@@ -33,20 +21,11 @@ class WorkflowRenderer:
                 {"workflow": plan.metadata_workflow_data}
             )
 
+        # Auto-discover helpers from generated_helpers.__all__ so new helpers
+        # are picked up without manually updating this list.
         func_strings = []
-        for func in [
-            _load_module,
-            _load_module_temp,
-            _is_comfyui_directory,
-            _find_from_extension_location,
-            get_value_at_index,
-            get_comfyui_path,
-            find_path,
-            add_comfyui_directory_to_sys_path,
-            add_extra_model_paths,
-            bootstrap_comfyui_runtime,
-            cleanup_comfyui_runtime,
-        ]:
+        for name in generated_helpers.__all__:
+            func = getattr(generated_helpers, name)
             func_strings.append(f"\n{inspect.getsource(func)}")
 
         static_imports = [