Review necessity of serialization utility functions

[seemenkina]

The utility functions in rln/src/utils.rs are used across various serialization functions, and tests for them exist in rln/tests/protocol.rs. However, it’s unclear whether all of these functions are actually necessary.

Tasks:

• Analyze the usage of each function in utils.rs to determine if they are all needed.
• Check if any functionality is redundant or can be optimized.
• Consider simplifying or removing unused functions if possible.

Possible but maybe doesn't make sense

• Benchmark different serialization approaches to compare performance.
• Check with other team members to see what serialization methods they are using and whether these functions align with them.

Suggested changes

1. Update this function regarding current version of RLN.
   

   zerokit/rln/src/protocol.rs

   Line 353 in 1930ca1

   pub fn prepare_prove_input(

Example:

zerokit/rln/src/public_api_tests.rs

Lines 696 to 706 in 1930ca1

	let mut serialized: Vec<u8> = Vec::new();
	serialized.append(&mut fr_to_bytes_le(&identity_secret_hash));
	serialized.append(&mut normalize_usize(identity_index));
	serialized.append(&mut fr_to_bytes_le(&user_message_limit));
	serialized.append(&mut fr_to_bytes_le(&Fr::from(1)));
	serialized.append(&mut fr_to_bytes_le(&utils_poseidon_hash(&[
	epoch,
	rln_identifier,
	])));
	serialized.append(&mut normalize_usize(signal.len()));
	serialized.append(&mut signal.to_vec());

2. Use this function inside test to avoid problem with serialisation
   

   zerokit/rln/src/protocol.rs

   Line 371 in 1930ca1

   pub fn prepare_verify_input(proof_data: Vec<u8>, signal: &[u8]) -> Vec<u8> {

One of place where need to replace:

zerokit/rln/src/public_api_tests.rs

Lines 724 to 730 in 1930ca1

	let mut proof_data = output_buffer.into_inner();
	// We prepare input for verify_rln_proof API
	// input_data is [ proof<128> | root<32> | external_nullifier<32> | x<32> | y<32> | nullifier<32> | signal_len<8> | signal<var> ]
	// that is [ proof_data || signal_len<8> | signal<var> ]
	proof_data.append(&mut normalize_usize(signal.len()));
	proof_data.append(&mut signal.to_vec());

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Related issue: #21