Add support for isize, usize scalars

Closes #1090

References:
  #1090
  https://stackoverflow.com/q/70232567/13977061

Author: simnalamburt

src/impl_ops.rs

@@ -336,6 +336,8 @@ mod arithmetic_ops {
     all_scalar_ops!(u32);
     all_scalar_ops!(i64);
     all_scalar_ops!(u64);
+    all_scalar_ops!(isize);
+    all_scalar_ops!(usize);
     all_scalar_ops!(i128);
     all_scalar_ops!(u128);