LWE: encode ciphertext RNS ring information for plaintext type

For concrete operation of ciphertext-plaintext in polynomial dialect, the plaintext type (i.e. NewLWEPlaintextType) should also record which `Z_Qi` it is in besides which `Z_t` it is in. We now have this information in IR via `mgmt.init`, but such information should then be inherited to the plaintext type.