feat: add leader command to flush cache

[Nashtare]

I figured it may be nice to have a command to flush stored circuits on disk, in case they accumulate and start blowing up disk usage, or even in case of discrepancies for cryptographers working on the constraints (as we only do a version-check through the Kernel code hash).

➜  zk_evm git:(clean_cache) ✗ ./target/release/leader --help
zero-bin leader config

Usage: leader [OPTIONS] <COMMAND>

Commands:
  clean  Deletes all the previously cached circuits
  stdio  Reads input from stdin and writes output to stdout
  rpc    Reads input from a node rpc and writes output to stdout
  http   Reads input from HTTP and writes output to a directory
  help   Print this message or the help of the given subcommand(s)

[0xaatif]

LGTM, I think this moves is away from the #447 direction though

[Nashtare]

LGTM, I think this moves is away from the #447 direction though

I don't disagree with this, although I strongly feel we need a mechanism for cache flushing, ideally something better than just manually doing rm -rf. Every time we re-generate, we store ~50GB of circuits on disk.