feat: Added prepare-inputs method to CLI that allows custom merging…

[mm-zk]

… of proof files.

What ❔

• A new option in airbender cli - that allows you to combine proofs into a single file (also with u32 integers in between).

cargo run --release -- prepare-inputs --inputs 4  /tmp/proof_1.json /tmp/proof_2.json --output-file /tmp/merged

This will create a /tmp/merged file with '4' (as u32) in first slot, and then data from first proof (in verifiable format) and then from the second.

Such file then can be fed into verifier or other program.