fix: N-02 Code Clarity Suggestions

[pscott]

• Use felt252 size and u8 size in the read/write storage code
• Use BoundedU8 instead of 255_u8
• Use ContractAddressZeroable for ContractAddressDefault
• Remove useless addition of with_prefix
• Simplify the deserialization in MerkleWhitelistVotingStrategy
• Return the components in a systematic order in uint256_into_le_u64s
• [ ] waiting for more information regarding Already Finalized error message
• Use is_non_zero() when possible

Closes #564

[Orland0x]

dude i just also did all of these ffs was about to push.

[pscott]

lmao frontran

[pscott]

thought u were working on https://github.com/snapshot-labs/sx-starknet/issues/555.. my bad, should've self assigned when i started. mb mb :(

[Orland0x]

assume they meant the 'Proposal has been finalized' message as thats the only one not like the others. i fixed on my branch

[pscott]

Superseeded by https://github.com/snapshot-labs/sx-starknet/pull/588