Add test that importing spatialmath does not load scipy

Add a test to ensure scipy is not loaded when importing spatialmath.

Author: RoboX2020

tests/test_import.py

@@ -0,0 +1,16 @@
+import subprocess
+import sys
+import unittest
+
+
+class TestImport(unittest.TestCase):
+    def test_import_does_not_load_scipy(self):
+        # scipy is slow to import and only a few functions need it, so it is
+        # imported by those functions and not when spatialmath is imported
+        code = "import sys, spatialmath; sys.exit(any(m.split('.')[0] == 'scipy' for m in sys.modules))"
+        result = subprocess.run([sys.executable, "-c", code])
+        self.assertEqual(result.returncode, 0, "import spatialmath loaded scipy")
+
+
+if __name__ == "__main__":  # pragma nocover
+    unittest.main()