Update variable names in ZK aff-g and fix minor typos

[jfdreis]

This PR aligns variable names in the implementation of the zk proof aff-g with the ones used in the specifications. See Issue #151 : Update paillier-zk so the variable names exactly match the spec.

Also fixed some typos in the specs.

Main chages

Specs	Implementation	This PR
E	C	E
N_j	key_j	n_j
N_i	key_i	n_i
l	l_x	l
l'	l_y	l_prime
rho	nonce	rho
rho_y	nonce_y	rho_y

Swapped lhs and rhs in the first and third checks to match the spec,s order.

Did not change

The variable challenge corresponds to alpha in the specs but remains challenge in the implementation for clarity. No changes were made to auxiliary data nor to documentation variables such as plaintext_x, ciphertext_x, etc.

ZKPs Matching the Specs

1. paillier_affine_operation_in_range.rs: variable names updated in this PR to match the specs.
2. dlog_with_el_gamal_commitment.rs: no changes needed if challenge and auxiliary data names remain as is.
3. no_small_factor.rs: already matches the specs, assuming the existing Data struct can remain unchanged.

[survived]

Hey @jfdreis, sorry for long response, I was waiting for private security fix #168 to be merged fist. I will look into PR this/next week!