lwe: add ciphertext size and clarify modulus types on new lwe types

[copybara-service]

lwe: add ciphertext size and clarify modulus types on new lwe types

This PR:

• Removes key identifier until we have the need for >1 "keyholder"
• Adds a ciphertext size descriping the "vectorspace" dimension of the ciphertexts (number of polynomials)
• Adds a description of how rings with RNS types look

[asraa]

@ZenithalHourlyRate @j2kun @AlexanderViand-Intel I made this PR to draft out the (1) addition of the size parameter and (2) to draft out our intentions about how RNS types fit into the modulus parameter in the ciphertext ring attribute and (3) the key attribute changes (removal of ID and size and clarification on basis)

Note that the description is hopeful for the polynomial dialect's ring change.

Do any of you have better nomenclature for the rotation basis / power of x basis in the key attribute? I didn't include a powers-of-s since it's not strictly necessary if we always perform rotations on canonical size 2 ciphertexts, but I borrowed the idea from @ZenithalHourlyRate PR #1067

[AlexanderViand-Intel]

Thanks for putting this together! I'd still love to have a "packet header breakdown" style diagram for the various attributes & types in the documentation ;) I'm happy to draw one up, though I'm not sure where it should live and if it should be an image (e.g., excalidraw) or ASCII so it can live directly in the tablegen docs?