Add (more? any?) tests for lwe.radd, lwe.rsub, lwe.rmul

[AlexanderViand-Intel]

While making some changes to the assembly format, I noticed a suspicious lack of failing tests, which makes me think there's no tests for these ops specifically (though they get exercised a lot in --scheme-to-openfhe). I'm pretty sure that's my fault, as I think I added the ops but did not add syntax/etc tests 🙈