Refine mres resolution length check for Singular

Adjust handling of mres to account for trailing zero module in Singular.

Author: cxzhong

src/sage/geometry/hyperplane_arrangement/arrangement.py

@@ -3472,7 +3472,20 @@ def is_free(self, algorithm='singular') -> bool:
         if algorithm == "singular":
             # TODO: Implement this using libSingular
             mres = self.defining_polynomial().jacobian_ideal()._singular_().mres(0)
-            return len(mres) <= 2
+            # Newer versions of Singular include a trailing zero module (R^0).
+            # Check if the last element is trivial and exclude it from the count.
+            resolution_length = len(mres)
+            if resolution_length > 0:
+                try:
+                    sing = mres.parent()
+                    last_elem = mres[resolution_length]
+                    # Check if this element is the zero module using size()
+                    size_val = int(sing.eval(f"size({last_elem.name()})"))
+                    if size_val == 0:  # Trailing zero module
+                        resolution_length -= 1
+                except:
+                    pass
+            return resolution_length <= 2
         elif algorithm == "BC":
             return self.derivation_module_free_chain() is not None
         else: