fix: clean up omnivoice import guard and __init__ error masking

Remove OmniVoice = None fallback in nodes/loader.py so missing omnivoice
gives a clear ImportError instead of a confusing AttributeError. Restore
__init__.py to clean form without the try/except that silently swallowed
real import errors. Add omnivoice mock to conftest.py and register a
pytest plugin that prevents pytest from treating the project root as a
Package node (which would try to import __init__.py outside a package
context and fail on the relative import).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

conftest.py

@@ -1,6 +1,31 @@
 import sys
 import os
+from pathlib import Path
+from unittest.mock import MagicMock
 
 # Ensure the project root is on sys.path so `nodes.loader` can be imported
 # as a top-level package without needing to install the package.
-sys.path.insert(0, os.path.dirname(__file__))
+_root = os.path.dirname(__file__)
+sys.path.insert(0, _root)
+
+# Mock omnivoice so it can be imported in tests without being installed
+sys.modules.setdefault("omnivoice", MagicMock())
+
+# Prevent pytest from treating the project root as a Python Package node.
+# The root __init__.py is a ComfyUI extension entrypoint that uses relative
+# imports and cannot be imported by pytest without a proper package context.
+# Overriding pytest_collect_directory stops pytest from creating a Package
+# node (and calling Package.setup() which imports __init__.py) for the root.
+class _RootDirPlugin:
+    """Registered as a plugin so it intercepts hooks before conftest scope limits."""
+
+    def pytest_collect_directory(self, path, parent):
+        from _pytest.main import Dir
+        if Path(path) == Path(_root):
+            # Return a plain Dir node instead of a Package node for the root,
+            # so pytest skips importing __init__.py during Package.setup().
+            return Dir.from_parent(parent, path=Path(path))
+
+
+def pytest_configure(config):
+    config.pluginmanager.register(_RootDirPlugin(), "_root_dir_plugin")