Support multi-block proving for other modes than Jerigon

[Nashtare]

#96 introduced multi-block processing with the Jerigon mode. While this is the mode to use in a real-life setting, testing & benchmarking are often performed in stdio mode (the former for easy reproducibility, the latter to not be impacted by networking conditions).

As such, it would be beneficial to also support multi block proving from this mode. We would probably need to enforce some rules on the witness files naming to ensure proper ordering when parsing.