Add runtime test with unused arguments

tests/run/unused.pyx

+cdef c_unused_simple(a, b, c):
+    """
+    >>> c_unused_simple(1, 2, 3)
+    3
+    """
+    return a + b
+
+cdef c_unused_optional(a, b, c=1, d=2):
+    """
+    >>> c_unused_optional(1, 2)
+    4
+    >>> c_unused_optional(1, 2, 3, 4)
+    6
+    """
+    return b + d
+
+cpdef cp_unused_simple(a, b, c):
+    """
+    >>> cp_unused_simple(1, 2, 3)
+    3
+    """
+    return a + b
+
+cpdef cp_unused_optional(a, b, c=1, d=2):
+    """
+    >>> cp_unused_optional(1, 2)
+    4
+    >>> cp_unused_optional(1, 2, 3, 4)
+    6
+    """
+    return b + d
+
+
+cdef class Unused:
+    """
+    >>> o = Unused()
+    """
+
+    cpdef cp_unused_simple(self, a, b, c):
+        return c
+
+    cpdef cp_unused_optional(self, a, b, c=1, d=2):
+        return b + d