[Diag] Print numpy + bundled OpenBLAS hash at pytest session start

Adds source/conftest.py so pytest dumps the resolved numpy version and the
bundled OpenBLAS .so filename at session start. Used by the negative/positive
arm validation PRs to capture which numpy bundle each CI test container ends
up with after isaaclab.sh --install completes.

The conftest.py imports numpy at module load. This is what pytest does
naturally via isaaclab module imports anyway -- making the import explicit
here only adds visibility, not crash conditions.

Author: hujc7

source/conftest.py

@@ -0,0 +1,23 @@
+# Copyright (c) 2022-2026, The Isaac Lab Project Developers (https://github.com/isaac-sim/IsaacLab/blob/main/CONTRIBUTORS.md).
+# All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+
+"""Dep-manifest diagnostic: prints numpy version + bundled OpenBLAS hash at pytest session start.
+
+Loaded by pytest when collecting tests under ``source/``. Importing numpy here registers
+its vendored OpenBLAS ``pthread_atfork`` handler in pytest's process, which is the same
+process that later calls ``fork()`` via ``SimulationApp()``. The output identifies which
+numpy + OpenBLAS bundle actually landed in each CI test container.
+"""
+
+import os
+
+import numpy
+
+print(f"\n[dep-manifest] numpy {numpy.__version__}", flush=True)
+_libs_dir = os.path.join(os.path.dirname(numpy.__file__), os.pardir, "numpy.libs")
+if os.path.isdir(_libs_dir):
+    for _f in sorted(os.listdir(_libs_dir)):
+        if "openblas" in _f.lower():
+            print(f"[dep-manifest] bundled openblas: {_f}", flush=True)