Optimize `num_bytes` and `hex_prefix_rlp`

[4l0n50]

We compute num_bytes by non-deterministically guessing the number of bits and checking that number >> number_of_bits - 1 == 1 (if number != 0). For hex_prefix_rlp, instead of writing the nibbles to the rlp segment one by one, we remove the first nibble (if necessary) directly on the packed nibbles and then write them using mstore_unpacking. For the ERC20 test, we get the following improvements on cpu and memory: CPU trace: 168206 -> 153563 Memory trace: 694042 -> 648593

[sonarcloud[bot]]

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