Add run_tests.bat/.sh to run the unittest suite via bin/

Follows the same setenv-based convention as the other bin/ scripts
and runs python -m unittest discover against tests/.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

bin/run_tests.sh

@@ -0,0 +1,8 @@
+#!/bin/bash
+# ================================================================
+# Fuehrt die unittest-Suite in tests/ aus
+# ================================================================
+
+source "$(dirname "${BASH_SOURCE[0]}")/setenv.sh"
+
+python -m unittest discover -s "$PLATZ/tests" -p "test_*.py" -v