test: add schematic tools tests and apply black formatting

- Add python/tests/conftest.py with MagicMock stubs for pcbnew/skip
- Add python/tests/test_schematic_tools.py with 29 tests covering
  WireManager.delete_wire, WireManager.delete_label (unit + integration),
  and parameter validation for all 11 new _handle_* methods
- Apply black formatting to component_schematic.py, wire_manager.py,
  and kicad_interface.py

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

python/tests/conftest.py

@@ -0,0 +1,26 @@
+"""
+Pytest configuration for python/tests.
+
+Sets up sys.path so that the python/ package root is importable without
+installing the project, and provides shared fixtures.
+"""
+import sys
+from pathlib import Path
+
+# Make the python/ package root importable
+PYTHON_ROOT = Path(__file__).parent.parent
+if str(PYTHON_ROOT) not in sys.path:
+    sys.path.insert(0, str(PYTHON_ROOT))
+
+# Stub out heavy KiCAD C-extension modules so tests can run without a real
+# KiCAD installation.  Extend this list whenever a new import fails.
+import types
+from unittest.mock import MagicMock
+
+# Use MagicMock so any attribute access (e.g. pcbnew.BOARD, pcbnew.LoadBoard)
+# returns another MagicMock rather than raising AttributeError.
+for _stub_name in ("pcbnew", "skip"):
+    if _stub_name not in sys.modules:
+        _m = MagicMock(spec_set=None)
+        _m.__name__ = _stub_name
+        sys.modules[_stub_name] = _m