maths: prefer brace value initialisation for almost_equal<int>

This is more likely to catch future issues with lossy transforms.

maths.hpp

@@ -106,7 +106,7 @@ namespace cruft {
                              std::is_signed_v<ValueA> == std::is_signed_v<ValueB>)
         {
             using common_t = std::common_type_t<ValueA,ValueB>;
-            return static_cast<common_t> (a) == static_cast<common_t> (b);
+            return common_t {a} == common_t {b};
         } else {
             return equal (a, b);
         }