feat(arithmetization): modify elf_to_json_gen to add ssz prefix as an independent blob at _input_start

[lorenzogentile404]

This is the current format of the JSON file taken as input by the RV interpreter written in zkc:

{
  "entry_point_and_blobs_count": "0x<entry_point:u64>_<blobs_count:u64>",
  "blobs_offset_and_size": "0x<blob0_offset:u64>_<blob0_size:u64>____<blob1_offset:u64>_<blob1_size:u64>____...",
  "blobs_data": "0x<blob0_bytes>____<blob1_bytes>____..."
}

When it comes to ssz files as input, we pre-process them to add at the beginning a 8 bytes prefix as LE containing the byte count of the ssz body.
We do not want to touch the ssz file, but instead just add that prefix at _input_start as an independent blob.
elf_to_json_gen is the script that needs to be edited.

[OlivierBBB]

I guess it's valid go if you were able to push it to the repo but wouldn't you wan to write

blobs := []memoryBlob{ memoryBlob{offset: inBytesOffset, data: prefix, name: "ssz_length"} }

instead ?

[lorenzogentile404]

The 2 are equivalent. In the first case, the outer keyword already defines what comes next, so the inner keyword can be omitted @OlivierBBB.

[OlivierBBB]

LGTM