PHASE 13.7.B: Linux platform compatibility fixes

safe_mode.py:
- Whitelist ROOT _process_root_events threads (Linux-only)
- Use substring matching for thread names

conftest.py:
- Add dfextensions parent path for sibling package imports
- Works in development mode and after pip install

test_safe_mode.py:
- Update assertion to match new error message

toy_nd.py:
- Add ensure_rvec_dictionaries() public API
- Extend detector layers from 7 to 18 (ITS2 + TPC)

run_tests.sh:
- Rename PHASE_BEGIN tag to PHASE_BEGIN_RDataFrameDSL

Test results: 2154 passed, 2 failed (99.9%)

Author: miranov25

UTILS/dfextensions/RDataFrameDSL/tests/conftest.py

@@ -33,6 +33,23 @@
 if _this_dir not in sys.path:
     sys.path.insert(0, _this_dir)
 
+# =============================================================================
+# Path Setup for dfextensions sibling packages (dfdraw, AliasDataFrame)
+# Only needed during development; unnecessary after pip install
+# =============================================================================
+
+from pathlib import Path
+
+try:
+    from dfextensions.dfdraw import DFDraw  # Check if already available (pip installed)
+except ImportError:
+    # Not pip-installed, add development path
+    # Path: tests/conftest.py -> tests/ -> RDataFrameDSL/ -> dfextensions/ -> UTILS/
+    _utils_dir = Path(__file__).resolve().parent.parent.parent.parent
+    if _utils_dir.exists() and str(_utils_dir) not in sys.path:
+        sys.path.insert(0, str(_utils_dir))
+
+
 # =============================================================================
 # Import invariant schema configuration
 # =============================================================================